PSLE
Pierre had a collection of notebooks, post-it pads and highlighters. He had 11 notebooks. 40% of his collection was post-it pads. He had 15 fewer post-it pads than highlighters.

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

(a)
40% = ⁴⁰₁₀₀ = ²₅

Number of post-it pads = 2 u
Number of highlighters = 2 u + 15
Number of notebooks = 11
Total number of items = 5 u

5 u = 2 u + 2 u + 15 + 11
5 u - 4 u = 26
1 u = 26

Number of post-it pads
= 2 u
= 2 x 26
= 52

(b)
Total number of items at first
= 5 u
= 5 x 26
= 130

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

Number of items after giving away some post-it pads
= 80% x 130
= ⁸⁰₁₀₀ x 130
= 104

Number of highlighters and notebooks
= 5 u - 2 u
= 3 u
= 3 x 26
= 78

Number of post-it pads left
= 104 - 78
= 26

Percentage of his collection that was post-it pads after that
= ²⁶₁₀₄ x 100%
= 25%

Answer(s): (a) 52; (b) 25%