PSLE
Betty and Justin bought storybooks at the prices shown below.

2 Large storybooks for $14
5 Small storybooks for $12

1. Betty bought an equal number of large and small storybooks. She spent $138 more on the large ones. How many storybooks did she buy altogether?
2. Justin 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 Betty bought is the same. Make the number of large and small storybooks the same. LCM of 2 and 5 is 10.

Cost of 2 large storybooks = $14
Cost of 10 large storybooks = 5 x 14 = $70

Cost of 5 small storybooks = $12
Cost of 10 small storybooks = 2 x 12 = $24

Difference in the cost of buying 10 small storybooks and 10 large storybooks
= 70 - 24
= $46

Number of sets of storybooks
= 138 ÷ 46
= 3

Number of storybooks that Betty bought
= 3 x 2 x 10
= 60

(b)
Justin 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 14 and 12 is 84.

Number of large storybooks that Justin bought
= 2 x (84 ÷ 14)
= 2 x 6
= 12

Number of the small storybooks that Justin bought
= 5 x (84 ÷ 12)
= 5 x 7
= 35

Fraction of the storybooks that Justin bought that were large
= ¹²_{12 + 35}
= ¹²₄₇

Answer(s): (a) 60; (b) ¹²₄₇