Page 40 - 新思维数学学生用书7 样章

2.2 Using expressions and formulae

Think like a mathematician

Work with a partner, or in a small group, to answer questions 6 and 7.
When you have answered the questions, discuss your answers with other groups.

6 Sanjay is paid $9 per hour. He writes this formula T = 9h.
a What do you think the letters h and T stand for?
b Write the formula in words.
c Work out the value of T when h = 30.

7 Every week, Yim pays for petrol and insurance for her car. She writes the formula
C = p + i.
a What do you think the letters C, p and i stand for?
b Write the formula in words.

c Work out the value of C when p = $25 and i = $7.

8 Jan calculates how much money he has left each week, using the
formula:

M = P – E, where: M is the money he has left over Tip
P is the money he is paid for working Jan’s expenses
E are his expenses
are things that

a Find the value of M when: he must pay for,
i P = $225 and E = $72 ii P = $178 and E = $36 such as food,
b Work out the value of P when M = $160 and E = $45. transport, bills,
Explain how you worked out your answer. etc.
9 A formula used in Science is:

V = IR, where: V is the voltage Tip
I is the current
R is the resistance IR means I × R.

Work out the value of V when:
a I = 3 and R = 7 b I = 4 and R = 9
You can use inverse operations to work out:
• the value of I if you know V and R

• the value of R if you know V and I.
c Work out the value of I when V = 30 and R = 6
d Work out the value of R when V = 40 and I = 5.

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