Page 37 - 新思维数学学生用书8 样章

2 Expressions, formulae and equations

Continued

Answer
a 2 × 5 + 4 × −2 Substitute x = 5 and y = −2 into the expression.

= 10 + −8 Work out 2 × 5 and 4 × −2.
= 10 − 8 = 2 Adding −8 is the same as subtracting 8.

b 3 × 10 + 4 Substitute x = 10 into the expression.
2
= 3 × 100 + 4 Work out 10 first.
2
= 300 + 4 = 304 Work out the multiplication before the addition.

c i hours = 24 × days There are 24 hours in every day.
ii h = 24d Use h for hours and d for days.

d h = 24 × 7 = 168 Substitute d = 7 into the formula.

e h = 24d The formula is h = 24 × d
h = d Use the inverse operation to make d the subject by dividing by
24 24.
d = h Rewrite the formula with the subject, d, on the left hand side.
24

Exercise 2.2

1 Copy and complete the working to find the value of each
expression.
a p + 5 when p = −3 p + 5 = −3 + 5 =

b q − 6 when q = 4 q − 6 = 4 − 6 =
c 6h when h = −3 6h = 6 × −3 =

d j when j = −20 j = − 20 =
4 4 4
e a + b when a = 6 and b = −3 a + b = 6 + −3 = 6 − 3 =

f c − d when c = 25 and d = 32 c − d = 25 − 32 =
2 Work out the value of each expression.
a 8m − 5 when m = −2 b 3z + v when z = 8 and v = −20
c 2x + 3y when x = 4 and y = 5 d 20 − 3n when n = 9

q
e u − 5 when u = 4 f p + when p = 30 and q = −8
2 5 2

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