Page 14 - 新思维数学活动用书8 样章

2.1 Constructing expressions

2 This box contains some books. When you double the
I double the number of books in the box. number, you × by 2.
Copy and complete the working to show how many
books are in the box now, when the box started with
a 3 books: 3 × 2 = b 5 books: 5 × 2 =

c 8 books: 8 × = d x books: x × = 2x
e y books: y × = f b books: b × =

3 This tin contains some sweets. When you halve the
I halve the number of sweets in the tin. number, you ÷ by 2.
Copy and complete the working to show how many

sweets are in the tin now, when the tin started with
a 4 sweets: 4 ÷ 2 = b 10 sweets: 10 ÷ 2 =
x
c 12 sweets: 12 ÷ = d x sweets: x ÷ =
2

e y sweets: y ÷ = f s sweets: s ÷ =
2
4 Zalika has a box that contains c one-dollar coins.
Choose the correct expression from the cloud to show c
the total number of one-dollar coins in the box when 2
a she takes 2 out c − 2
b she puts 2 more in c + 2

c she takes out half of the coins 2c
d she doubles the number of coins in the box.
5 Match each description on the left with the correct expression on

the right.
The first one is done for you: A and v
A Multiply n by 3 and subtract 8 i 3(n + 8)

B Add 8 and n then multiply by 3 ii 8(n + 3)
C Multiply n by 3 and add 8 iii 3(n − 8)

D Add 3 and n then multiply by 8 iv 8(n − 3)
E Subtract 3 from n then multiply by 8 v 3n − 8

F Subtract 8 from n then multiply by 3 vi 3n + 8

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