PSLE
Simon had a collection of markers, rulers and correction tapes. He had 15 markers. 40% of his collection was rulers. He had 12 fewer rulers than correction tapes.

1. How many rulers did Simon have?
2. Simon 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 correction tapes = 2 u + 12
Number of markers = 15
Total number of items = 5 u

5 u = 2 u + 2 u + 12 + 15
5 u - 4 u = 27
1 u = 27

Number of rulers
= 2 u
= 2 x 27
= 54

(b)
Total number of items at first
= 5 u
= 5 x 27
= 135

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

Number of items after giving away some rulers
= 80% x 135
= ⁸⁰₁₀₀ x 135
= 108

Number of correction tapes and markers
= 5 u - 2 u
= 3 u
= 3 x 27
= 81

Number of rulers left
= 108 - 81
= 27

Percentage of his collection that was rulers after that
= ²⁷₁₀₈ x 100%
= 25%

Answer(s): (a) 54; (b) 25%