"Protecting Swans" PPT Courseware 10

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"Protecting Swans" PPT Courseware 10

Oral calculation

6×2 = 20×4 =

6×20 = 10×4 =

6×200 = 5×4 =

What is the expansion of 1.6 to 10 times its original size?

6×10=60

2.6 What is the expansion to 100 times the original size?

6×100=600

Summary: Multiplying a number by a number can also be said to expand the number to several times its original value.

The changing pattern of product

When two numbers are multiplied, one factor remains unchanged, the other factor is multiplied by something, and the product must also be multiplied by something.

According to 8×50=400, write the product directly.

(8×2) (400×2)

16×50＝800

(8×4) (400×4)

32×50=1600

When two numbers are multiplied, one factor remains unchanged, the other factor is divided by a number, and the product is also divided by a number.

Can you combine these two laws?

When two numbers are multiplied, one factor remains unchanged, the other factor is multiplied by something, and the product must also be multiplied by something.

When two numbers are multiplied, one factor remains unchanged, the other factor is multiplied by a certain number (or divided by a certain number), and the product is multiplied by a certain number (or divided by a certain number).

When two numbers are multiplied, one factor remains unchanged, the other factor is divided by a number, and the product is also divided by a number.

Mathematics Arena

Level 1: Fierce Eyes

1. Judgment:

(1) When two numbers are multiplied, if one factor remains unchanged and the other factor is multiplied by 5, the product should be multiplied by 4. ( )

(2) When two numbers are multiplied, one factor is divided by 10, the other factor remains unchanged, and the product is also divided by 10. ( )

Level 2: Flexibility and resourcefulness

Find the rules and write down the numbers.

12×8＝96 40×21＝840

12×16＝192 40×7＝280

12×32＝384 20×21＝420

Summary of rules:

When two factors are multiplied, one factor is expanded to m times and the other factor is expanded to n times, then the product is expanded to m × n times.

Multiplying two factors, one factor is divided by m and the other factor is divided by n, then the product is divided by (m × n)

Do the math, think about it. What patterns can you spot?

36×18=648

(36÷2)×(18×2)=648

(36÷4)×(18×4)=648

(36×3)×(18÷3)=648

When two numbers are multiplied together, one factor is multiplied by a certain number and the other factor is divided by a certain number at the same time, and the product remains unchanged.

Are the following questions correct?

Expand 10 by 8 times to get 88 ( )

The product of two factors is 56. If one factor is divided by 7 and the other factor remains unchanged, the resulting product is 392. ( )

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Update Time: 2024-10-27

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