PSLE
Mark had a collection of rulers, folders and glues. He had 49 rulers. 30% of his collection was folders. He had 43 fewer folders than glues.

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

(a)
30% = ³⁰₁₀₀ = ³₁₀

Number of folders = 3 u
Number of glues = 3 u + 43
Number of rulers = 49
Total number of items = 10 u

10 u = 3 u + 3 u + 43 + 49
10 u - 6 u = 92
4 u = 92

1 u = 92 ÷ 4 = 23

Number of folders
= 3 u
= 3 x 23
= 69

(b)
Total number of items at first
= 10 u
= 10 x 23
= 230

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

Number of items after giving away some folders
= 80% x 230
= ⁸⁰₁₀₀ x 230
= 184

Number of glues and rulers
= 10 u - 3 u
= 7 u
= 7 x 23
= 161

Number of folders left
= 184 - 161
= 23

Percentage of his collection that was folders after that
= ²³₁₈₄ x 100%
= 12.5%

Answer(s): (a) 69; (b) 12.5%