PSLE
Peter had a collection of highlighters, pens and notebooks. He had 11 highlighters. 40% of his collection was pens. He had 18 fewer pens than notebooks.

1. How many pens did Peter have?
2. Peter gave away some pens. His total collection decreased by 20%. What percentage of his collection was pens after that?

(a)
40% = ⁴⁰₁₀₀ = ²₅

Number of pens = 2 u
Number of notebooks = 2 u + 18
Number of highlighters = 11
Total number of items = 5 u

5 u = 2 u + 2 u + 18 + 11
5 u - 4 u = 29
1 u = 29

Number of pens
= 2 u
= 2 x 29
= 58

(b)
Total number of items at first
= 5 u
= 5 x 29
= 145

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

Number of items after giving away some pens
= 80% x 145
= ⁸⁰₁₀₀ x 145
= 116

Number of notebooks and highlighters
= 5 u - 2 u
= 3 u
= 3 x 29
= 87

Number of pens left
= 116 - 87
= 29

Percentage of his collection that was pens after that
= ²⁹₁₁₆ x 100%
= 25%

Answer(s): (a) 58; (b) 25%