PSLE
Ryan had red staplers and black staplers for sale. He sold 270 red staplers. 40% of the staplers sold were black.

1. How many red staplers and black staplers did Ryan sell altogether?
2. He sold 50% of his staplers. 75% of the staplers left unsold were red. How many black staplers did Ryan have at first?

	Red	Black	Total	Total in percent
Before	6.75 u	3.25 u	10 u	100%
Change	- 60% - 3 u	- 40% - 2 u	- 100% - 5 u	- 50%
After	75% 3.75 u	25% 1.25 u	100% 5 u	50%

40% = ⁴⁰₁₀₀ = ²₅

Total number of staplers sold = 5 u
Number of black staplers sold = 2 u

Number of red staplers sold
= 5 u - 2 u
= 3 u

3 u = 270

1 u = 270 ÷ 3 = 90

Total number of staplers sold
= 5 u
= 5 x 90
= 450

(b)
Percent of the staplers left unsold
= 100% - 50%
= 50%

50% of the staplers that were sold = 5 u
50% of the staplers that were left unsold = 5 u

Percent of the staplers left unsold that were red = 75%
Percent of the staplers left unsold that were black = 100% - 75% = 25%

Number of the staplers left unsold that were black
= 25% x 5 u
= ²⁵₁₀₀ x 5 u
= 1.25 u

Number of black staplers that Ryan had at first
= 1.25 u + 2 u
= 3.25 u
= 3.25 x 90
= 292.5

Answer(s): (a) 450; (b) 292.5