Page 33 - 新思维数学学生用书8 样章

2 Expressions, formulae and equations

10 a Write an expression for each description.
i one-half of x add 8
ii three-quarters of x subtract 12
iii 7 add four-fifths of x
iv 20 subtract five-ninths of x
b Describe each expression in words.

i x + 2 ii 5x − 4 iii 8 − 2x iv 3 + 7x
6 7 3 8
11 This is part of Maya’s homework.

Question
Write an expression for 1 a cm
3
a the perimeter of this rectangle
b the area of this rectangle. 4b cm
Answers
1
1
2
a perimeter = a + a + 4b + 4b = a + 8b cm
3 3 3
1
4
b area = a × 4b = ab cm 2
3 3
Use Maya’s method to write an expression for the perimeter and

area of each of these rectangles. Simplify each expression.

a b
1 a cm 3 d cm
2 5

6b cm 7c cm

Activity 2.1

Work with a partner.
Take it in turns to say ‘Write an expression for …’ and give a description

like those in Question 10a.
For example, ‘Write an expression for two-thirds of x add 9.’
Your partner must write the expression correctly.
Check their expression. If it is correct, they score 1 point.

Write five expressions each, then check the scores!

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