PSLE
Nick had a collection of pens, files and post-it pads. He had 240 pens. 15% of his collection was files. He had 40 fewer files than post-it pads.

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

(a)
15% = ¹⁵₁₀₀ = ³₂₀

Number of files = 3 u
Number of post-it pads = 3 u + 40
Number of pens = 240
Total number of items = 20 u

20 u = 3 u + 3 u + 40 + 240
20 u - 6 u = 280
14 u = 280

1 u = 280 ÷ 14 = 20

Number of files
= 3 u
= 3 x 20
= 60

(b)
Total number of items at first
= 20 u
= 20 x 20
= 400

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

Number of items after giving away some files
= 80% x 400
= ⁸⁰₁₀₀ x 400
= 320

Number of post-it pads and pens
= 20 u - 3 u
= 17 u
= 17 x 20
= 340

Number of files left
= 320 - 340
= 20

Percentage of his collection that was files after that
= ²⁰₃₂₀ x 100%
= 6.25%

Answer(s): (a) 60; (b) 6.25%