PSLE
Ben had black notebooks and pink notebooks for sale. He sold 560 black notebooks. 30% of the notebooks sold were pink.

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

	Black	Pink	Total	Total in percent
Before	14.5 u	5.5 u	20 u	100%
Change	- 70% - 7 u	- 30% - 3 u	- 100% - 10 u	- 50%
After	75% 7.5 u	25% 2.5 u	100% 10 u	50%

30% = ³⁰₁₀₀ = ³₁₀

Total number of notebooks sold = 10 u
Number of pink notebooks sold = 3 u

Number of black notebooks sold
= 10 u - 3 u
= 7 u

7 u = 560

1 u = 560 ÷ 7 = 80

Total number of notebooks sold
= 10 u
= 10 x 80
= 800

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

50% of the notebooks that were sold = 10 u
50% of the notebooks that were left unsold = 10 u

Percent of the notebooks left unsold that were black = 75%
Percent of the notebooks left unsold that were pink = 100% - 75% = 25%

Number of the notebooks left unsold that were pink
= 25% x 10 u
= ²⁵₁₀₀ x 10 u
= 2.5 u

Number of pink notebooks that Ben had at first
= 2.5 u + 3 u
= 5.5 u
= 5.5 x 80
= 440

Answer(s): (a) 800; (b) 440