Page 51 - 新思维数学学生用书9 样章

2 Expressions and formulae

7 In some countries, the mass of
(

a person is measured in stones (S) K = 514 S + P) where: K is the number of kilograms
11
and pounds (P). S is the number of stones
The formula to convert a mass P is the number of pounds.
from stones and pounds to

kilograms is shown. Tip
Work out the mass, in kilograms, of a person with a mass of 9 stones exactly
a 10 stones and 3 pounds b 7 stones and 10 pounds means 9 stones
c 15 stones and 1 pound d 9 stones. and 0 pounds.

Think like a mathematician

8 Work with a partner to answer this question.

a Make x the subject of each of these formulae.
Write down if A, B or C is the correct answer.
i y = 2x + z A x = y + z B x = y − z C x = y − z
2 2 2
h
ii y = 5 x − 3h A x = 2 y + 3h B x = 2 y − 6h C x = 2( y + 3 )
2 5 5 5
iii y =+ x A x = 7k(y – 6) B x = 7ky – 6 C x = 7k(y + 6)
6
7k
iv y = x − m A x = 3n y − m B x = 3n y C x = 3n y + m
3 n m
v y = w – 7x A x = w − y B x = y + w C x = y − w
7 7 7
b Discuss with your partner and with other learners in the class.
Explain what mistakes have been made to get the incorrect answers.

9 Make t the subject of each of these formulae.
a m = 7t + 9 b k = t − m c p = h + t d q = 5 t − w
5 v 9
10 The diagram shows a shape made from a square and a rectangle.

a
c

b a
a Write a formula for the area (A) of the shape.

b Work out A when a = 6, b = 3 and c = 4.5.
c Show that you can rearrange your formula to give a = Abc.
−
d Work out a when A = 80, b = 8 and c = 2.

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