PSLE
Nora and Carl bought jigsaw puzzles at the prices shown below.

4 Large jigsaw puzzles for $15
5 Small jigsaw puzzles for $9

1. Nora bought an equal number of large and small jigsaw puzzles. She spent $156 more on the large ones. How many jigsaw puzzles did she buy altogether?
2. Carl spent an equal amount of money on the large and small jigsaw puzzles. What fraction of the jigsaw puzzles he bought were large?

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

Cost of 4 large jigsaw puzzles = $15
Cost of 20 large jigsaw puzzles = 5 x 15 = $75

Cost of 5 small jigsaw puzzles = $9
Cost of 20 small jigsaw puzzles = 4 x 9 = $36

Difference in the cost of buying 20 small jigsaw puzzles and 20 large jigsaw puzzles
= 75 - 36
= $39

Number of sets of jigsaw puzzles
= 156 ÷ 39
= 4

Number of jigsaw puzzles that Nora bought
= 4 x 2 x 20
= 160

(b)
Carl spent an equal amount of money on the large and small jigsaw puzzles.  Make the amount of money spent on the large and small jigsaw puzzles the same.
LCM of 15 and 9 is 45.

Number of large jigsaw puzzles that Carl bought
= 4 x (45 ÷ 15)
= 4 x 3
= 12

Number of the small jigsaw puzzles that Carl bought
= 5 x (45 ÷ 9)
= 5 x 5
= 25

Fraction of the jigsaw puzzles that Carl bought that were large
= ¹²_{12 + 25}
= ¹²₃₇

Answer(s): (a) 160; (b) ¹²₃₇