PSLE
Erika and Valen bought storybooks at the prices shown below.

4 Large storybooks for $6
7 Small storybooks for $4

1. Erika bought an equal number of large and small storybooks. She spent $78 more on the large ones. How many storybooks did she buy altogether?
2. Valen 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 Erika bought is the same. Make the number of large and small storybooks the same. LCM of 4 and 7 is 28.

Cost of 4 large storybooks = $6
Cost of 28 large storybooks = 7 x 6 = $42

Cost of 7 small storybooks = $4
Cost of 28 small storybooks = 4 x 4 = $16

Difference in the cost of buying 28 small storybooks and 28 large storybooks
= 42 - 16
= $26

Number of sets of storybooks
= 78 ÷ 26
= 3

Number of storybooks that Erika bought
= 3 x 2 x 28
= 168

(b)
Valen 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 6 and 4 is 12.

Number of large storybooks that Valen bought
= 4 x (12 ÷ 6)
= 4 x 2
= 8

Number of the small storybooks that Valen bought
= 7 x (12 ÷ 4)
= 7 x 3
= 21

Fraction of the storybooks that Valen bought that were small
= ²¹_{8 + 21}
= ²¹₂₉

Answer(s): (a) 168; (b) ²¹₂₉