Page 33 - 新思维数学活动用书9 样章

2 Expressions and formulae

b The formula to work out the total number of days (T) in w weeks and d days is T = 7w + d.
Use the formula to work out the total number of days in
i 2 weeks and 5 days ii 6 weeks and 3 days.
5 Copy and complete the workings to make b the subject of each formula.
The first one has been done for you.

a A = bh A = b × h swap sides: b × h = A reverse the ×: b = A
h

b F = bg F = b × g swap sides: b × = reverse the ×: b =

c T = mb T = m × b swap sides: × = reverse the ×: b =

d X = b + rt swap sides: b + rt = reverse the +: b = X −

e M = b − kn swap sides: b − = reverse the −: b = +

Practice
6 a Use the formula D = ST to work out the value of D when
i S = 50 and T = 3 ii S = 120 and T = 1.5.

b Rearrange the formula D = ST to make S the subject.
Work out the value of S when D = 100 and T = 5.
c Rearrange the formula D = ST to make T the subject.
Work out the value of T when D = 22 and S = 4.

7 Stanley is d years old. Polly is 3 years older than Stanley.
Max is 2 years younger than Stanley.

a Write an expression for Polly’s age and Max’s age in terms of d.
b Write a formula for the total age, T, of Stanley, Polly and Max.
c Use your formula in part b to work out the value of T when d = 8.
d Rearrange your formula in part b to make d the subject.

e Use your formula in part d to work out the value of d when T = 34.
8 Use the formula F = I + ae to work out the value of
a F when I = 5, a = 10 and e = 2 Tip

b F when I = 0, a = 9 and e = 6 In parts c, d and e,
c I when F = 100, a = 4 and e = 15 start by changing
d e when F = 50, I = 10 and a = 8 the subject of the

e a when F = 48, I = 34 and e = 2. formula.

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