Page 39 - 新思维数学学生用书8 样章

2 Expressions, formulae and equations

7 This is how a taxi company works out the cost of a journey for a customer:

There is a fixed charge of $6 plus $2 per kilometre.
a Write a formula for the cost of a journey, in
i words ii letters.
b Use your formula in part a ii to work out the cost of a journey of 35 km.
8 Use the formula v = u + 10t to work out the value of v when

a u = 5 and t = 12 b u = 8 and t = 15 c u = 0 and t = 20.
9 Use the formula F = ma to work out F when
a m = 6 and a = 2 b m = 18 and a = 3 c m = 8 and a = −4.

10 The height of a horse is measured in hands (H) and inches (I).
This formula is used to work out the height of a horse in centimetres (C ).
C = 2.5(4H + I) where: C is the number of centimetres
H is the number of hands
I is the number of inches.

Sasha has a horse with a height of 16 hands and 1 inch.
She uses the formula to work out the height of her horse, in centimetres.

C = 2.5(4 × 16 + 1)

= 2.5(64 + 1) Tip
= 2.5 × 65 16 hands exactly
= 162.5 cm means 16 hands
and 0 inches.

Work out the height, in centimetres, of a horse with height
a 14 hands and 2 inches b 15 hands and 3 inches
c 13 hands and 1 inch d 17 hands and 2 inches

e 16 hands f 12 hands.

Would it matter if the formula used the letters D, E and F instead of C, H and I?
Do the letters help you to understand a formula? Explain your answer.

11 Use the formula C = πd to Tip

a estimate the value of C when d = 19 m
b calculate the value of C when d = 19 m. Remember that π
Give your answer to one decimal place. is approximately
3.14.

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