PSLE
Barbara and Seth bought storybooks at the prices shown below.

4 Large storybooks for $10
7 Small storybooks for $4

1. Barbara bought an equal number of large and small storybooks. She spent $216 more on the large ones. How many storybooks did she buy altogether?
2. Seth 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 Barbara 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 = $10
Cost of 28 large storybooks = 7 x 10 = $70

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
= 70 - 16
= $54

Number of sets of storybooks
= 216 ÷ 54
= 4

Number of storybooks that Barbara bought
= 4 x 2 x 28
= 224

(b)
Seth 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 10 and 4 is 20.

Number of large storybooks that Seth bought
= 4 x (20 ÷ 10)
= 4 x 2
= 8

Number of the small storybooks that Seth bought
= 7 x (20 ÷ 4)
= 7 x 5
= 35

Fraction of the storybooks that Seth bought that were small
= ³⁵_{8 + 35}
= ³⁵₄₃

Answer(s): (a) 224; (b) ³⁵₄₃