PSLE
Will had a collection of rulers, post-it pads and glues. He had 163 rulers. 15% of his collection was post-it pads. He had 19 fewer post-it pads than glues.

1. How many post-it pads did Will have?
2. Will gave away some post-it pads. His total collection decreased by 20%. What percentage of his collection was post-it pads after that?

(a)
15% = ¹⁵₁₀₀ = ³₂₀

Number of post-it pads = 3 u
Number of glues = 3 u + 19
Number of rulers = 163
Total number of items = 20 u

20 u = 3 u + 3 u + 19 + 163
20 u - 6 u = 182
14 u = 182

1 u = 182 ÷ 14 = 13

Number of post-it pads
= 3 u
= 3 x 13
= 39

(b)
Total number of items at first
= 20 u
= 20 x 13
= 260

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

Number of items after giving away some post-it pads
= 80% x 260
= ⁸⁰₁₀₀ x 260
= 208

Number of glues and rulers
= 20 u - 3 u
= 17 u
= 17 x 13
= 221

Number of post-it pads left
= 208 - 221
= 13

Percentage of his collection that was post-it pads after that
= ¹³₂₀₈ x 100%
= 6.25%

Answer(s): (a) 39; (b) 6.25%