PSLE
Michael had blue notebooks and pink notebooks for sale. He sold 330 blue notebooks. 40% of the notebooks sold were pink.

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

	Blue	Pink	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 notebooks sold = 5 u
Number of pink notebooks sold = 2 u

Number of blue notebooks sold
= 5 u - 2 u
= 3 u

3 u = 330

1 u = 330 ÷ 3 = 110

Total number of notebooks sold
= 5 u
= 5 x 110
= 550

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

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

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

Number of the notebooks left unsold that were pink
= 25% x 5 u
= ²⁵₁₀₀ x 5 u
= 1.25 u

Number of pink notebooks that Michael had at first
= 1.25 u + 2 u
= 3.25 u
= 3.25 x 110
= 357.5

Answer(s): (a) 550; (b) 357.5