PSLE
Shiyun and Luis bought pillows at the prices shown below.

2 Large pillows for $7
3 Small pillows for $4

1. Shiyun bought an equal number of large and small pillows. She spent $39 more on the large ones. How many pillows did she buy altogether?
2. Luis spent an equal amount of money on the large and small pillows. What fraction of the pillows he bought were large?

(a)
Number of large and small pillows that Shiyun bought is the same. Make the number of large and small pillows the same. LCM of 2 and 3 is 6.

Cost of 2 large pillows = $7
Cost of 6 large pillows = 3 x 7 = $21

Cost of 3 small pillows = $4
Cost of 6 small pillows = 2 x 4 = $8

Difference in the cost of buying 6 small pillows and 6 large pillows
= 21 - 8
= $13

Number of sets of pillows
= 39 ÷ 13
= 3

Number of pillows that Shiyun bought
= 3 x 2 x 6
= 36

(b)
Luis spent an equal amount of money on the large and small pillows.  Make the amount of money spent on the large and small pillows the same.
LCM of 7 and 4 is 28.

Number of large pillows that Luis bought
= 2 x (28 ÷ 7)
= 2 x 4
= 8

Number of the small pillows that Luis bought
= 3 x (28 ÷ 4)
= 3 x 7
= 21

Fraction of the pillows that Luis bought that were large
= ⁸_{8 + 21}
= ⁸₂₉

Answer(s): (a) 36; (b) ⁸₂₉