PSLE
Luke had red notebooks and purple notebooks for sale. He sold 840 red notebooks. 30% of the notebooks sold were purple.

1. How many red notebooks and purple notebooks did Luke sell altogether?
2. He sold 50% of his notebooks. 80% of the notebooks left unsold were red. How many purple notebooks did Luke have at first?

	Red	Purple	Total	Total in percent
Before	15 u	5 u	20 u	100%
Change	- 70% - 7 u	- 30% - 3 u	- 100% - 10 u	- 50%
After	80% 8 u	20% 2 u	100% 10 u	50%

30% = ³⁰₁₀₀ = ³₁₀

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

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

7 u = 840

1 u = 840 ÷ 7 = 120

Total number of notebooks sold
= 10 u
= 10 x 120
= 1200

(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 red = 80%
Percent of the notebooks left unsold that were purple = 100% - 80% = 20%

Number of the notebooks left unsold that were purple
= 20% x 10 u
= ²⁰₁₀₀ x 10 u
= 2 u

Number of purple notebooks that Luke had at first
= 2 u + 3 u
= 5 u
= 5 x 120
= 600

Answer(s): (a) 1200; (b) 600