PSLE
Mark had a collection of pens, rulers and pencils. He had 14 pens. 40% of his collection was rulers. He had 14 fewer rulers than pencils.

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

(a)
40% = ⁴⁰₁₀₀ = ²₅

Number of rulers = 2 u
Number of pencils = 2 u + 14
Number of pens = 14
Total number of items = 5 u

5 u = 2 u + 2 u + 14 + 14
5 u - 4 u = 28
1 u = 28

Number of rulers
= 2 u
= 2 x 28
= 56

(b)
Total number of items at first
= 5 u
= 5 x 28
= 140

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

Number of items after giving away some rulers
= 80% x 140
= ⁸⁰₁₀₀ x 140
= 112

Number of pencils and pens
= 5 u - 2 u
= 3 u
= 3 x 28
= 84

Number of rulers left
= 112 - 84
= 28

Percentage of his collection that was rulers after that
= ²⁸₁₁₂ x 100%
= 25%

Answer(s): (a) 56; (b) 25%