Page 39 - 新思维数学学生用书7 样章

2 Expressions, formulae and equations

c 10 _ x when x = 3 d 2m + n when m = 7 and n = 6
_
10 _ x = 10 3 2m + n = 2 × 7 + 6
= = + 6

=

e 7x when = 5 f ab _ c when a = 9, b = 8 and c = 32
x
_
7x = 7 × 5 ab _ c = 9 × 8 32

= = − 32
=

2 Work out the value of each expression.

a a + 5 when a = 3 b x – 9 when x = 20
c f + g when f = 7 and g = 4 d m – n when m = 100 and n = 25
e 3k when k = 5 f p + 2q when p = 5 and q = 3

g 2h + 3t when h = 8 and t = 5 h y when y = 32
4
i 30 _ 2 when c = 6 j x + y when x = 19 and y = 11
c 2
3 Raul writes a formula for the number of hours in any number of days.
He writes: number of hours = 24 × number of days
a Explain why this formula is correct.
b Write the formula using letters. Use h for hours and d for days.
c Use your formula to work out the number of hours in five days.

4 a Write a formula for the number of minutes in any number of hours, in:
i words ii letters
b Use your formula in part a ii to work out the number of minutes in five hours.

5 Kristina goes out for a meal at a restaurant with four friends. They share the total cost of the
meal equally between the five of them.
a Write a formula to work out the amount they each pay, in:
i words ii letters
b Use your formula in part a ii to work out the amount they each pay when the total cost of

the meal is $85.

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