PSLE
Gillian and Fred bought storybooks at the prices shown below.

3 Large storybooks for $12
4 Small storybooks for $9

1. Gillian bought an equal number of large and small storybooks. She spent $42 more on the large ones. How many storybooks did she buy altogether?
2. Fred spent an equal amount of money on the large and small storybooks. What fraction of the storybooks he bought were large?

(a)
Number of large and small storybooks that Gillian bought is the same. Make the number of large and small storybooks the same. LCM of 3 and 4 is 12.

Cost of 3 large storybooks = $12
Cost of 12 large storybooks = 4 x 12 = $48

Cost of 4 small storybooks = $9
Cost of 12 small storybooks = 3 x 9 = $27

Difference in the cost of buying 12 small storybooks and 12 large storybooks
= 48 - 27
= $21

Number of sets of storybooks
= 42 ÷ 21
= 2

Number of storybooks that Gillian bought
= 2 x 2 x 12
= 48

(b)
Fred 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 12 and 9 is 36.

Number of large storybooks that Fred bought
= 3 x (36 ÷ 12)
= 3 x 3
= 9

Number of the small storybooks that Fred bought
= 4 x (36 ÷ 9)
= 4 x 4
= 16

Fraction of the storybooks that Fred bought that were large
= ⁹_{9 + 16}
= ⁹₂₅

Answer(s): (a) 48; (b) ⁹₂₅