PSLE
Perry had a collection of folders, files and rulers. He had 13 folders. 40% of his collection was files. He had 11 fewer files than rulers.

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

(a)
40% = ⁴⁰₁₀₀ = ²₅

Number of files = 2 u
Number of rulers = 2 u + 11
Number of folders = 13
Total number of items = 5 u

5 u = 2 u + 2 u + 11 + 13
5 u - 4 u = 24
1 u = 24

Number of files
= 2 u
= 2 x 24
= 48

(b)
Total number of items at first
= 5 u
= 5 x 24
= 120

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

Number of items after giving away some files
= 80% x 120
= ⁸⁰₁₀₀ x 120
= 96

Number of rulers and folders
= 5 u - 2 u
= 3 u
= 3 x 24
= 72

Number of files left
= 96 - 72
= 24

Percentage of his collection that was files after that
= ²⁴₉₆ x 100%
= 25%

Answer(s): (a) 48; (b) 25%