PSLE
Oliver had a collection of notebooks, post-it pads and markers. He had 373 notebooks. 15% of his collection was post-it pads. He had 19 fewer post-it pads than markers.

1. How many post-it pads did Oliver have?
2. Oliver gave away some post-it pads. His total collection decreased by 20%. What percentage of his collection was post-it pads after that?

(a)
15% = ¹⁵₁₀₀ = ³₂₀

Number of post-it pads = 3 u
Number of markers = 3 u + 19
Number of notebooks = 373
Total number of items = 20 u

20 u = 3 u + 3 u + 19 + 373
20 u - 6 u = 392
14 u = 392

1 u = 392 ÷ 14 = 28

Number of post-it pads
= 3 u
= 3 x 28
= 84

(b)
Total number of items at first
= 20 u
= 20 x 28
= 560

Total collection in the end in percent
= 100% - 20%
= 80%

Number of items after giving away some post-it pads
= 80% x 560
= ⁸⁰₁₀₀ x 560
= 448

Number of markers and notebooks
= 20 u - 3 u
= 17 u
= 17 x 28
= 476

Number of post-it pads left
= 448 - 476
= 28

Percentage of his collection that was post-it pads after that
= ²⁸₄₄₈ x 100%
= 6.25%

Answer(s): (a) 84; (b) 6.25%