PSLE
Seth had a collection of files, markers and highlighters. He had 283 files. 15% of his collection was markers. He had 11 fewer markers than highlighters.

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

(a)
15% = ¹⁵₁₀₀ = ³₂₀

Number of markers = 3 u
Number of highlighters = 3 u + 11
Number of files = 283
Total number of items = 20 u

20 u = 3 u + 3 u + 11 + 283
20 u - 6 u = 294
14 u = 294

1 u = 294 ÷ 14 = 21

Number of markers
= 3 u
= 3 x 21
= 63

(b)
Total number of items at first
= 20 u
= 20 x 21
= 420

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

Number of items after giving away some markers
= 80% x 420
= ⁸⁰₁₀₀ x 420
= 336

Number of highlighters and files
= 20 u - 3 u
= 17 u
= 17 x 21
= 357

Number of markers left
= 336 - 357
= 21

Percentage of his collection that was markers after that
= ²¹₃₃₆ x 100%
= 6.25%

Answer(s): (a) 63; (b) 6.25%