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The purpose of the lesson:
- In a fun way, introduce students to the rule of multiplying a decimal fraction by a natural number, by a bit unit and the rule of expressing a decimal fraction as a percentage. Develop the ability to apply the acquired knowledge in solving examples and problems.
- To develop and activate the logical thinking of students, the ability to identify patterns and generalize them, strengthen memory, the ability to cooperate, provide assistance, evaluate their work and the work of each other.
- To cultivate interest in mathematics, activity, mobility, ability to communicate.
Equipment: interactive board, a poster with a cyphergram, posters with mathematicians' statements.
During the classes
- Organizing time.
- Oral counting is a generalization of previously studied material, preparation for the study of new material.
- Explanation of new material.
- Homework assignment.
- Mathematical physical education.
- Generalization and systematization of the acquired knowledge in a playful way with the help of a computer.
- Grading.
2. Guys, today our lesson will be somewhat unusual, because I will not spend it alone, but with my friend. And my friend is also unusual, now you will see him. (A cartoon computer appears on the screen.) My friend has a name and he can talk. What's your name, friend? Komposha replies: "My name is Komposha." Are you ready to help me today? YES! Well then, let's start the lesson.
Today I received an encrypted cyphergram, guys, which we must solve and decipher together. (A poster is posted on the board with an oral account for adding and subtracting decimal fractions, as a result of which the guys get the following code 523914687. )
| 5 | 2 | 3 | 9 | 1 | 4 | 6 | 8 | 7 |
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
Komposha helps to decipher the received code. As a result of decoding, the word MULTIPLICATION is obtained. Multiplication is the keyword of the topic of today's lesson. The topic of the lesson is displayed on the monitor: “Multiplying a decimal fraction by a natural number”
Guys, we know how the multiplication of natural numbers is performed. Today we will consider the multiplication of decimal numbers by a natural number. The multiplication of a decimal fraction by a natural number can be considered as the sum of terms, each of which is equal to this decimal fraction, and the number of terms is equal to this natural number. For example: 5.21 3 \u003d 5.21 + 5, 21 + 5.21 \u003d 15.63 So 5.21 3 = 15.63. Representing 5.21 as an ordinary fraction of a natural number, we get
And in this case, we got the same result of 15.63. Now, ignoring the comma, let's take the number 521 instead of the number 5.21 and multiply by the given natural number. Here we must remember that in one of the factors the comma is moved two places to the right. When multiplying the numbers 5, 21 and 3, we get a product equal to 15.63. Now, in this example, we will move the comma to the left by two digits. Thus, by how many times one of the factors was increased, the product was reduced by so many times. Based on the similar points of these methods, we draw a conclusion.
To multiply a decimal by a natural number, you need:
1) ignoring the comma, perform the multiplication of natural numbers;
2) in the resulting product, separate with a comma on the right as many characters as there are in a decimal fraction.
The following examples are displayed on the monitor, which we analyze together with Komposha and the guys: 5.21 3 = 15.63 and 7.624 15 = 114.34. After I show multiplication by a round number 12.6 50 \u003d 630. Next, I turn to the multiplication of a decimal fraction by a bit unit. Showing the following examples: 7,423 100 \u003d 742.3 and 5.2 1000 \u003d 5200. So, I introduce the rule for multiplying a decimal fraction by a bit unit:
To multiply a decimal fraction by bit units 10, 100, 1000, etc., it is necessary to move the comma to the right in this fraction by as many digits as there are zeros in the bit unit record.
I end the explanation with the expression of a decimal fraction as a percentage. I enter the rule:
To express a decimal as a percentage, multiply it by 100 and add the % sign.
I give an example on a computer 0.5 100 \u003d 50 or 0.5 \u003d 50%.
4. At the end of the explanation, I give the guys homework, which is also displayed on the computer monitor: № 1030, № 1034, № 1032.
5. In order for the guys to rest a little, to consolidate the topic, we do a mathematical physical education session together with Komposha. Everyone stands up, shows the class the solved examples and they must answer whether the example is correct or incorrect. If the example is solved correctly, then they raise their hands above their heads and clap their palms. If the example is not solved correctly, the guys stretch their arms to the sides and knead their fingers.
6. And now you have a little rest, you can solve the tasks. Open your textbook to page 205, № 1029. in this task it is necessary to calculate the value of expressions:
Tasks appear on the computer. As they are solved, a picture appears with the image of a boat, which, when fully assembled, sails away.
No. 1031 Calculate:
Solving this task on a computer, the rocket gradually develops, solving the last example, the rocket flies away. The teacher gives a little information to the students: “Every year, spaceships take off to the stars from the Kazakhstani land from the Baikonur Cosmodrome. Near Baikonur, Kazakhstan is building its new Baiterek cosmodrome.
No. 1035. Task.
How far will a car travel in 4 hours if the speed of the car is 74.8 km/h.
This task is accompanied by sound design and displaying a brief condition of the task on the monitor. If the problem is solved, right, then the car starts to move forward to the finish flag.
№ 1033. Write decimals as percentages.
0,2 = 20%; 0,5 = 50%; 0,75 = 75%; 0,92 = 92%; 1,24 =1 24%; 3,5 = 350%; 5,61= 561%.
Solving each example, when the answer appears, a letter appears, resulting in the word Well done.
The teacher asks Komposha, why would this word appear? Komposha replies: “Well done, guys!” and say goodbye to everyone.
The teacher sums up the lesson and assigns grades.
In this article, we will consider such an action as multiplying decimal fractions. Let's start with the formulation of general principles, then we will show how to multiply one decimal fraction by another and consider the method of multiplication by a column. All definitions will be illustrated with examples. Then we will analyze how to correctly multiply decimal fractions by ordinary, as well as by mixed and natural numbers (including 100, 10, etc.)
As part of this material, we will only touch on the rules for multiplying positive fractions. Cases with negative numbers are discussed separately in the articles on the multiplication of rational and real numbers.
Let us formulate the general principles that must be followed when solving problems on the multiplication of decimal fractions.
To begin with, let us recall that decimal fractions are nothing more than a special form of writing ordinary fractions, therefore, the process of their multiplication can be reduced to the same for ordinary fractions. This rule works for both finite and infinite fractions: after converting them to ordinary fractions, it is easy to perform multiplication with them according to the rules we have already studied.
Let's see how such tasks are solved.
Example 1
Compute the product of 1.5 and 0.75.
Solution: First, replace the decimal fractions with ordinary ones. We know that 0.75 is 75/100 and 1.5 is 1510. We can reduce the fraction and extract the whole part. We will write the result 125 1000 as 1 , 125 .
Answer: 1 , 125 .
We can use the column counting method as we do for natural numbers.
Example 2
Multiply one periodic fraction 0 , (3) by another 2 , (36) .
First, let's reduce the original fractions to ordinary ones. We will be able to:
0 , (3) = 0 , 3 + 0 , 03 + 0 , 003 + 0 , 003 + . . . = 0 , 3 1 - 0 , 1 = 0 , 3 9 = 3 9 = 1 3 2 , (36) = 2 + 0 , 36 + 0 , 0036 + . . . = 2 + 0 , 36 1 - 0 , 01 = 2 + 36 99 = 2 + 4 11 = 2 4 11 = 26 11
Therefore, 0 , (3) 2 , (36) = 1 3 26 11 = 26 33 .
The resulting ordinary fraction can be reduced to decimal form by dividing the numerator by the denominator in a column:
Answer: 0 , (3) 2 , (36) = 0 , (78) .
If we have infinite non-periodic fractions in the condition of the problem, then we need to perform their preliminary rounding (see the article on rounding numbers if you forgot how this is done). After that, you can perform the multiplication operation with already rounded decimal fractions. Let's take an example.
Example 3
Compute the product of 5 , 382 ... and 0 , 2 .
Solution
We have an infinite fraction in the problem, which must first be rounded to hundredths. It turns out that 5, 382 ... ≈ 5, 38. Rounding the second factor to hundredths does not make sense. Now you can calculate the desired product and write down the answer: 5, 38 0, 2 = 538 100 2 10 = 1 076 1000 = 1, 076.
Answer: 5.382… 0.2 ≈ 1.076.
The column counting method can be applied not only to natural numbers. If we have decimals, we can multiply them in exactly the same way. Let's derive the rule:
Definition 1
Multiplication of decimal fractions by a column is performed in 2 steps:
1. We perform multiplication by a column, not paying attention to commas.
2. We put a decimal point in the final number, separating it as many digits on the right side as both factors contain decimal places together. If as a result there are not enough numbers for this, we add zeros on the left.
We will analyze examples of such calculations in practice.
Example 4
Multiply the decimals 63, 37 and 0, 12 by a column.
Solution
First of all, let's do the multiplication of numbers, ignoring the decimal points.
Now we need to put a comma in the right place. It will separate the four digits on the right side since the sum of the decimal places in both factors is 4 . You don't have to add zeros, because signs are enough.
Answer: 3.37 0.12 = 7.6044.
Example 5
Calculate how much is 3.2601 times 0.0254.
Solution
We count without commas. We get the following number:
We will put a comma separating 8 digits on the right side, because the original fractions together have 8 decimal places. But our result has only seven digits, and we can't do without extra zeros:
Answer: 3.2601 0.0254 = 0.08280654.
How to multiply a decimal by 0.001, 0.01, 01, etc
You often have to multiply decimals by such numbers, so it is important to be able to do this quickly and accurately. We write down a special rule that we will use in such multiplication:
Definition 2
If we multiply a decimal by 0, 1, 0, 01, etc., we end up with a number that looks like the original fraction, with the decimal point moved to the left by the required number of places. If there are not enough digits to transfer, you need to add zeros on the left.
So, to multiply 45, 34 by 0, 1, the comma must be moved in the original decimal fraction by one sign. We end up with 4,534.
Example 6
Multiply 9.4 by 0.0001.
Solution
We will have to move the comma to four digits according to the number of zeros in the second factor, but the numbers in the first are not enough for this. We assign the necessary zeros and get that 9, 4 0, 0001 = 0, 00094.
Answer: 0 , 00094 .
For infinite decimals, we use the same rule. So, for example, 0 , (18) 0 , 01 = 0 , 00 (18) or 94 , 938 … 0 , 1 = 9 , 4938 … . and etc.
The process of such a multiplication is no different from the action of multiplying two decimal fractions. It is convenient to use the multiplication method in a column if the condition of the problem contains a final decimal fraction. In this case, it is necessary to take into account all the rules that we talked about in the previous paragraph.
Example 7
Calculate how much will be 15 2, 27.
Solution
Multiply the original numbers by a column and separate the two commas.
Answer: 15 2.27 = 34.05.
If we perform the multiplication of a periodic decimal fraction by a natural number, we must first change the decimal fraction to an ordinary one.
Example 8
Compute the product of 0 , (42) and 22 .
We bring the periodic fraction to the form of an ordinary fraction.
0 , (42) = 0 , 42 + 0 , 0042 + 0 , 000042 + . . . = 0 , 42 1 - 0 , 01 = 0 , 42 0 , 99 = 42 99 = 14 33
0 , 42 22 = 14 33 22 = 14 22 3 = 28 3 = 9 1 3
The final result can be written as a periodic decimal fraction as 9 , (3) .
Answer: 0 , (42) 22 = 9 , (3) .
Infinite fractions must be rounded before counting.
Example 9
Calculate how much will be 4 2 , 145 ... .
Solution
Let's round up to hundredths the original infinite decimal fraction. After that, we will come to the multiplication of a natural number and a final decimal fraction:
4 2, 145 ... ≈ 4 2, 15 = 8, 60.
Answer: 4 2.145 ... ≈ 8.60.
How to multiply a decimal by 1000, 100, 10, etc.
Multiplying a decimal fraction by 10, 100, etc. is often found in problems, so we will analyze this case separately. The basic multiplication rule is:
Definition 3
To multiply a decimal by 1000, 100, 10, etc., you need to move its comma by 3, 2, 1 digits depending on the multiplier and discard extra zeros on the left. If there are not enough digits to move the comma, we add as many zeros to the right as we need.
Let's show an example how to do it.
Example 10
Do the multiplication of 100 and 0.0783.
Solution
To do this, we need to move the decimal point by 2 digits to the right. We end up with 007 , 83 The zeros on the left can be discarded and the result can be written as 7 , 38 .
Answer: 0.0783 100 = 7.83.
Example 11
Multiply 0.02 by 10 thousand.
Solution: we will move the comma four digits to the right. In the original decimal fraction, we do not have enough signs for this, so we have to add zeros. In this case, three 0's will suffice. As a result, it turned out 0, 02000, move the comma and get 00200, 0. Ignoring the zeros on the left, we can write the answer as 200 .
Answer: 0.02 10,000 = 200.
The rule we have given will also work in the case of infinite decimal fractions, but here you should be very careful about the period of the final fraction, since it is easy to make a mistake in it.
Example 12
Compute the product of 5.32 (672) times 1000 .
Solution: first of all, we will write the periodic fraction as 5, 32672672672 ..., so the probability of making a mistake will be less. After that, we can move the comma to the desired number of characters (three). As a result, we get 5326 , 726726 ... Let's put the period in brackets and write the answer as 5 326 , (726) .
Answer: 5 . 32 (672) 1000 = 5 326 . (726) .
If in the conditions of the problem there are infinite non-periodic fractions that must be multiplied by ten, one hundred, one thousand, etc., do not forget to round them before multiplying.
To perform this type of multiplication, you need to represent the decimal fraction as an ordinary fraction and then follow the already familiar rules.
Example 13
Multiply 0 , 4 by 3 5 6
Solution
Let's first convert the decimal to a common fraction. We have: 0 , 4 = 4 10 = 2 5 .
We got the answer as a mixed number. You can write it as a periodic fraction 1, 5 (3) .
Answer: 1 , 5 (3) .
If an infinite non-periodic fraction is involved in the calculation, you need to round it up to a certain number and only then multiply it.
Example 14
Calculate the product of 3.5678. . . 2 3
Solution
We can represent the second factor as 2 3 = 0, 6666 …. Next, we round both factors to the thousandth place. After that, we will need to calculate the product of two final decimal fractions 3.568 and 0.667. Let's count the column and get the answer:
The final result must be rounded to thousandths, since it was to this category that we rounded the original numbers. We get that 2.379856 ≈ 2.380.
Answer: 3, 5678. . . 2 3 ≈ 2.380
If you notice a mistake in the text, please highlight it and press Ctrl+Enter
What is the issue about?
What is known?
What to find?
Express 3 rubles 8 kopecks in rubles. How much will it be? (3.08 rubles)
How to find? What action? (by multiplication)
Can we find? (no)
What skills do we lack to solve this problem?
(multiply decimal fractions by a natural number)
Formulate the topic of the lesson. And write down the subject and date in your notebook
So what should we learn today?
We will answer the question at the end of the lesson.
Motivation: why is this knowledge necessary?
in science and industry, in agriculture and everyday life, decimal fractions are used much more often than ordinary ones. This is due to the simplicity of the calculation rules, their similarity to the rules of operations with natural numbers. Therefore, you need to learn how to multiply decimal fractions.
So, take off the white hat, put on the green one.
What is the source of knowledge?
Where can we find the answer to our question? Of course it's a book. Open the textbook page 204.
Find the rule for multiplying a decimal by a natural number. Read. Tell the rule to each other.
Well done guys, good job. Now we take off the green hat and put on the yellow one. Who will try to tell the rule for everyone?
To multiply a decimal by a natural number, you need:
1) multiply it by this number, ignoring the comma;
2) in the resulting product, separate with a comma as many digits on the right as there are separated by a comma in a decimal fraction.
I show you how to write. Multiply 1.83 by 4
Write the reference diagram in your notebook:
action plan:
Sign the numbers one below the other, ignoring the comma
Multiply like natural numbers
Determine the number of digits after the decimal point in the product
Separate the desired number of digits in the product with a comma from right to left
And now let's check how you understood the rule. We solve in a notebook and on the board. No. 1306 (1 column)
Guys, but there are examples that do not need to be written in a column. They can be counted orally. Here we will try now. But there are some rules: you can’t speak, shout, get up from your seat. If the answer is correct, raise the red hat, if it is incorrect, the blue one. And the higher you raise your hat, the better
Mental counting "Find the mistake"
0.7 * 2=0.14 blue
0.15 * 3=0.45 red
0.2 * 23=4.6 red
1.6 * 4=0.64 blue
0.12 * 3=0.36 red
3.21*3=96.3 blue
2*1.44=28.8 blue
7 * 1.11=7.77 red
What knowledge did you apply when solving these examples? (multiply dec. Fractions by nat. Number)
Well done, you showed how quickly and correctly you can count.
Well done boys! I hope each of you remember these rules and will be able to apply them in the future.
Well, now back to the problem that confronted us at the beginning of the lesson. What is this problem? (1 student at the blackboard)
Let's remember what the task sounds like?
1 kilowatt-hour of electricity costs 3 rubles 08 kopecks. How many rubles do you need to pay for electricity if 364 kilowatts burned up in a month?
Let's see, now is there enough knowledge for us to solve this problem? (Yes) what knowledge should help us?
3.08 * 364 \u003d 1121.12 (rub.) - pay for the month
Answer; 1121.12 rubles
Here we have solved this problem. Now you can help your parents with the calculations.
So what knowledge did you apply to solve this problem? (multiply des. Fractions by nat. Number)
We take off the yellow hat, put on black. Our task is to learn how to perform multiplication, assess the risks. That is, to identify places where you can make a mistake.
Perform multiplication by commenting on the solution
(work in groups on cards of 4 people. You know the rules for working in a group!
1. Find a piece:
A) 3 . 8.3 \u003d 24.9 (1B.)
B) 35 . 1.7 \u003d 59.5 (1B.)
B) 173 . 0.19 = 32.87 (1B.)
(2b.) All sides of the hexagon have the same length 6.83 cm. Find the perimeter of the hexagon.
Answer: 40.98
5 points - "5"
4 points - "4"
3 points - "3"
Gymnastics for the eyes 2min
Guys, I suggest you get up from your desks and have a little rest. We follow the hats with our eyes.
They did the job well. Now we have to check how we learned to perform multiplication.
Let's think about what kind of hat we need now? Agree, yellow. Guys, now take the cards that are on your desks. Now apply your knowledge to this task (do it yourself)
Card work: Knowing what the work is
398 * 51=20298 put the correct comma
39,8 * 51=20298
0,0398 * 51=20298
3,98 * 51=20298
0,398 * 51=20298
Completed, and now exchange cards with a neighbor. Look at the board, I gave you the correct answers. Check. Change back. Raise your hand who hasn't made a single mistake.
Now let's see if you can apply the new rule yourself. To do this, I offer you a small test, during which you must compose a word. The work of each of you will be appreciated. So let's get started.
Variant test.
Handing over test papers. Raise your hand who made the word. What word came out? Well done and great. So you got a five.
I'm glad for your grades.
So guys. We put on a blue hat.
What did we learn in the lesson? What problem was posed in the lesson? (Find out how much you need to pay per month for electricity)
Were we able to solve it? (yes)
To consolidate the acquired knowledge, you need to do your homework. d / z perform to the best of your ability p. 204, p. 34, learn the rules,
"5" - No. 1331, 1330, come up with tasks from life for multiplying des. Fraction on nat. number
"4" - No. 1330, 1331 and filling out the receipt
"3" - No. 1330
View the readings of the electric meter, write down these readings and ask the parents what the price is for 1 kW / h and the meter readings in the previous month. Ask your parents how to fill out a receipt, what needs to be done for this, how to find the amount of electricity that has been consumed for the current month. Fill out a receipt.
Long awaited call.
The lesson starts.
Today we will be again
Solve, guess, dare!
Show me and the guests with what mood you came to the lesson.
We will try to improve it during the lesson.
Guys! I am glad to see you at the lesson today in a good mood.
Look into each other's eyes, smile, wish your comrade a good working mood with your eyes.
I also wish you good work today.
Guys! What topic are we working on?
What do we know about this topic?
And what does it mean?
What else do you know?
Formulate it.
Can you add something else about knowledge on this topic?
And how should this be done?
Well done boys!
And now we'll see how you can do it, how you apply the rules.(See Presentation, slide #2 and 3)
Solve the anagram and eliminate the extra word.
(See Presentation, slide #4 and 5)
Which of these words do you think is superfluous?
And why? How do you think?
Well done boys!
Remember how these terms are spelled correctly.
Guys! What do you think, have we solved all types of tasks on this topic?
We continue to consolidate the topic “Multiplying a decimal fraction by a natural number”.
Define the objectives of the lesson.
Where do we start?
What will be the next steps?
PI
memory
33
1. Solving the example on your own in pairs with mutual verification
(See Presentation, slide #6)
2...Problem solution:Nyusha ate 3 pieces of cake, 0.65 kg each, and Barash ate 10 portions of cake, 0.84 kg each. How much cake did they eat? How much more cake did Barash eat than Nyusha?See the presentation, slide number 7)
Let's look at the solution of the problem and compare it with our own.
See the presentation, slide number 8)
3. Entertaining page - task
Solving the problem of ingenuity
See the presentation, slide number 9-11)
4. Solving equations on your own (2 optional) with self-checking of the answer and solution for the presentation
See the presentation, slide number 12 - 15)
Let's cheer up our body a little. Please stand near your desks and repeat after me:
Hands raised and waved
The trees are making noise.
To the sides of the hand and waved
The birds are flying towards us.
Quickly sat down, hands folded
The animals are sitting in the mink.
Everyone got up and quietly sat down at their desks.
Children want to learn.
Group work
Task: Solve the examples orally and match the correct answer.
Distribute the worksheet to each group. The tasks are the same.
Checking the completed task.
See the presentation, slide number 16)
Let's summarize today's lesson.
Have we fully implemented the plan?
Did our work meet the objectives of the lesson?
What did you expect from today's lesson?
What caused the difficulty?
Were there any tasks that you enjoyed doing?
What knowledge gained earlier was needed at the lesson today?
And what do you think, the knowledge gained today in the lesson will be necessary for you in the next lessons.
You rate your
mood at the end of the lesson.
Lesson grades.
Write down your homework in your diary:
P.134 (repeat the rules),
Differentiated task
Public lesson
Topic: Multiplication of decimal fractions by natural numbers
5th grade
Goals:
Educational: c improve the ability to multiply a decimal fraction by a natural number and continue to work on the technique of multiplying a decimal fraction by 10, 100, 1000.
Developing: to develop mathematical speech in students, to promote the development of independence, the ability to evaluate their work.
Educational: to cultivate interest in mathematics, discipline, responsible attitude to educational work.
Teaching methods: verbal, visual, practical.
Form of study: individual, group.
Equipment: The lesson is held in a classroom with a computer and a projector.
During the classes:
Org. moment (checking readiness for the lesson) (1 minute)
Knowledge update (10 minutes)
#1 (1 minute)
No. 2 (1 minute)
Compare decimals:
14.2 and 14.20
8.7 and 8.608
10.72 and 10.719
0.095 and 0.1
174.1 and 174.097
56.567 and 45.567
12.45 and 12.456
№ 3 (1 minute)
Arrange the numbers in ascending order:
3,2; 3,07; 7,021; 5,7; 7,23; 5,07; 7,2; 5,75
Solution:
3,07; 3,2; 5,07; 5,7; 5,75; 7,021; 7,2; 7,23
#4 (1 minute)
Today we will perform various tasks in the lesson, multiply decimal fractions by natural numbers, multiply decimal fractions by 10, 100,1000 solve problems, and by solving tasks we will find out which living creatures are listed in the Red Book.
No. 5 verbally (3 minutes)
№ 1317
Find the value of the expression:
a) 2.7-0.6=2.1
b) 3.5+2.3=5.8
c) 5.8-1.9=3.9
d) 0.69+0=0.69
e) 3.6+0.8=4.4
f) 7.1-0=7.1
g) 4.9+6.3=11.2
h) 0.84-0.22=0.62
No. 1318 (g-z)
Calculate:
d) 0.57+0.3= 0,87
e) 1.36+2.0=3.36
e) 2.45-1.3= 1,15
g) 3+0.24= 3,24
h) 2-0.6= 1,4
No. 1310 (oral) 3 minutes
a) 6.42*10=64.2
b) 6.387*100=638.7
c) 45.48*1000=45480
0,00081*1000=0,81
0,102*10000=1020
3 Problem solving
Solve the equations: (2 students are called to the board for 3 minutes)
(x-0.5):8=0.3
x -0.5=0.3*8
Answer: x=2.9
V) x: 5 + 1.1 = 2.5
x::5 = 2.5-1.1
x:5=1.4
x=1.4*5
Answer x=7
Physical education (2 minutes)
One two three four five -
Once! Get up and stretch.
Two! Bend over, unbend.
Three! Three claps in the hands
Three head nods.
Four - arms wider.
Five - wave your hands.
Six - sit quietly at the desk.
No. 4 (3 minutes)
Find the value of the expression:
M 1,2+1,2=1,2*2=2,4
E 3,5+3,5+3,5=3,5*3=10,5
W 2,36+2,36+2,36+2,36=2,36*4=9,44
ABOUT 5,1+5,1+5,1=5,1*3=15,3
H 1,4+1,4=1,4*2=2,8
AND 8,54+8,54+8,54+8,54=8,54*4=34,16
A 0,12+0,12+0,12+0,12+0,12=0,12*5=0, 6
Task (5 minutes)
№ 1313
Piglet ate 3 jars of honey, 0.65 kg each, and Winnie the Pooh - 10 pots of honey, 0.84 kg each. How much honey did they eat? How much more honey did Winnie the Pooh eat than Piglet?
Questions:
1) What is said about Piglet?
2) What is said about Winnie the Pooh?
3) How to find how much honey Piglet ate?
4) How to find how much honey Winnie the Pooh ate?
5) How much more honey did Winnie the Pooh eat than Piglet?
Solution:
Piglet ate 3*0.65=1.95 (kg) of honey
10*0.84=8.4 (kg) Winnie the Pooh ate honey.
1.95+8.4=10.35(kg) of honey they ate together
8.4-1.95=6.45(kg) per 6.45 kg of honey Winnie the Pooh ate more than Piglet.
№ 1306 (E, F, G, I, K) (8 minutes)
E) 25.85*98=2533.3
25,85*(100-2)=25,85*100-25,85*2=2585-51,7=2533,3
25,85*(90+8)=25,85*90+8* 25,85=2326,5+206,8=2533,3
G) 4.55*6*7=27.3*7=191.1
H) 12.344*15*16=185.16*16=2962.56
I) (2.8+5.3)*12=8.1*12=97.2
(2,8+5,3)*12=2,8*12+5,3*12=33,6+63,6=97,2
K) (8.7-4.3) * 15 \u003d 4.4 * 15 \u003d 66
(8,7-4,3)*15=8,7*15-4.3*15=130,5-64,5=66
2533,3
185,16
191,1
2962,56
97,2
31,85
Summing up, assessments, homework (printout) 2 minutes
Homework:
Find a piece:
2) The road consists of 3 sections. The length of the first section is 8.4 km, the second section is 2 times longer than the length of the first section and 3 km less than the length of the third section. What is the length of the whole road.
3) Find the value of the expression using the distributive property of multiplication:
a) 36*0.17+36*0.33
