PSLE
Sean had silver notebooks and purple notebooks for sale. He sold 30 silver notebooks. 40% of the notebooks sold were purple.

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

	Silver	Purple	Total	Total in percent
Before	7 u	3 u	10 u	100%
Change	- 60% - 3 u	- 40% - 2 u	- 100% - 5 u	- 50%
After	80% 4 u	20% 1 u	100% 5 u	50%

40% = ⁴⁰₁₀₀ = ²₅

Total number of notebooks sold = 5 u
Number of purple notebooks sold = 2 u

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

3 u = 30

1 u = 30 ÷ 3 = 10

Total number of notebooks sold
= 5 u
= 5 x 10
= 50

(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 Sean had at first
= 1 u + 2 u
= 3 u
= 3 x 10
= 30

Answer(s): (a) 50; (b) 30