PSLE
Joelle and Wesley bought storybooks at the prices shown below.

4 Large storybooks for $15
5 Small storybooks for $12

1. Joelle bought an equal number of large and small storybooks. She spent $81 more on the large ones. How many storybooks did she buy altogether?
2. Wesley spent an equal amount of money on the large and small storybooks. What fraction of the storybooks he bought were small?

(a)
Number of large and small storybooks that Joelle bought is the same. Make the number of large and small storybooks the same. LCM of 4 and 5 is 20.

Cost of 4 large storybooks = $15
Cost of 20 large storybooks = 5 x 15 = $75

Cost of 5 small storybooks = $12
Cost of 20 small storybooks = 4 x 12 = $48

Difference in the cost of buying 20 small storybooks and 20 large storybooks
= 75 - 48
= $27

Number of sets of storybooks
= 81 ÷ 27
= 3

Number of storybooks that Joelle bought
= 3 x 2 x 20
= 120

(b)
Wesley spent an equal amount of money on the large and small storybooks. Make the amount of money spent on the large and small storybooks the same.
LCM of 15 and 12 is 60.

Number of large storybooks that Wesley bought
= 4 x (60 ÷ 15)
= 4 x 4
= 16

Number of the small storybooks that Wesley bought
= 5 x (60 ÷ 12)
= 5 x 5
= 25

Fraction of the storybooks that Wesley bought that were small
= ²⁵_{16 + 25}
= ²⁵₄₁

Answer(s): (a) 120; (b) ²⁵₄₁