PSLE
Luis had a collection of rulers, correction tapes and punchers. He had 15 rulers. 40% of his collection was correction tapes. He had 15 fewer correction tapes than punchers.

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

(a)
40% = ⁴⁰₁₀₀ = ²₅

Number of correction tapes = 2 u
Number of punchers = 2 u + 15
Number of rulers = 15
Total number of items = 5 u

5 u = 2 u + 2 u + 15 + 15
5 u - 4 u = 30
1 u = 30

Number of correction tapes
= 2 u
= 2 x 30
= 60

(b)
Total number of items at first
= 5 u
= 5 x 30
= 150

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

Number of items after giving away some correction tapes
= 80% x 150
= ⁸⁰₁₀₀ x 150
= 120

Number of punchers and rulers
= 5 u - 2 u
= 3 u
= 3 x 30
= 90

Number of correction tapes left
= 120 - 90
= 30

Percentage of his collection that was correction tapes after that
= ³⁰₁₂₀ x 100%
= 25%

Answer(s): (a) 60; (b) 25%