Page 28 - Mathematics Coursebook

2.4 Constructing expressions

3 Write an expression for the answer to each of these.
a David has x DVDs. He buys 6 more.
How many DVDs does he now have?
b Molly is m years old and Barney is b years old.
What is the total of their ages?
c Ted can store g photographs on one memory card.
How many photographs can he store on 3 memory cards
of the same size?

4 Maliha thinks of a number, x.
Write an expression for the number Maliha gets when she:
a multiplies the number by 3 b multiplies the number by 4 then adds 1
c divides the number by 3 d divides the number by 2 then subtracts 9.
5 The cost of an adult’s ticket into a theme park is $a.
The cost of a child’s ticket into the same theme park is $c.
Write an expression for the total cost for each group.
a 1 adult and 1 child b 2 adults and 1 child c 4 adults and 5 children
6 This is part of Shashank’s homework.

Question
Adrian thinks of a number, n.
Write an expression for the number Adrian gets when he:
a a adds 2 to the number then multiplies by 5
b subtracts 3 from the number then divides by 2.
You must use
Solution brackets if you add
a (n + 2) × 5 which can be written as 5(n + 2) or subtract before
n <3
b (n – 3) ÷ 2 which can be written as n multiplying or
2 dividing.

Use Shashank’s method to write an expression for the number Adrian gets when he:
Use Shashank’s method to write an expression for the number Adrian gets when he:
a adds 5 to the number then multiplies by 3 b adds 7 to the number then divides by 4

c subtracts 2 from the number then divides by 5 d subtracts 9 from the number then multiplies by 8.
7 Match each description (in the left-hand column) to the correct expression (in the right-hand column).
a Multiply n by 3 and subtract from 2 i 2 + 3n
2
b Add 2 and n then multiply by 3 ii 2 + < n
3
c Multiply n by 3 and subtract 2 iii 2 − 3n
d Multiply n by 3 and add 2 iv 3n − 2

e Add 2 and n then divide by 3 v 3(n + 2)
f Divide n by 3 and add 2 vi 2 < n
3
vii n 2
3
Write a description for the expression that is left over.

2 Sequences, expressions and formulae 27