PSLE
Ben had green notebooks and silver notebooks for sale. He sold 90 green notebooks. 40% of the notebooks sold were silver.

1. How many green notebooks and silver notebooks did Ben sell altogether?
2. He sold 50% of his notebooks. 60% of the notebooks left unsold were green. How many silver notebooks did Ben have at first?

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

40% = ⁴⁰₁₀₀ = ²₅

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

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

3 u = 90

1 u = 90 ÷ 3 = 30

Total number of notebooks sold
= 5 u
= 5 x 30
= 150

(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 green = 60%
Percent of the notebooks left unsold that were silver = 100% - 60% = 40%

Number of the notebooks left unsold that were silver
= 40% x 5 u
= ⁴⁰₁₀₀ x 5 u
= 2 u

Number of silver notebooks that Ben had at first
= 2 u + 2 u
= 4 u
= 4 x 30
= 120

Answer(s): (a) 150; (b) 120