PSLE
Carl had silver notebooks and purple notebooks for sale. He sold 160 silver notebooks. 60% of the notebooks sold were purple.

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

	Silver	Purple	Total	Total in percent
Before	6 u	4 u	10 u	100%
Change	- 40% - 2 u	- 60% - 3 u	- 100% - 5 u	- 50%
After	80% 4 u	20% 1 u	100% 5 u	50%

60% = ⁶⁰₁₀₀ = ³₅

Total number of notebooks sold = 5 u
Number of purple notebooks sold = 3 u

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

2 u = 160

1 u = 160 ÷ 2 = 80

Total number of notebooks sold
= 5 u
= 5 x 80
= 400

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

Number of the notebooks left unsold that were purple
= 20% x 5 u
= ²⁰₁₀₀ x 5 u
= 1 u

Number of purple notebooks that Carl had at first
= 1 u + 3 u
= 4 u
= 4 x 80
= 320

Answer(s): (a) 400; (b) 320