PSLE
Simon had green notebooks and blue notebooks for sale. He sold 420 green notebooks. 30% of the notebooks sold were blue.

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

	Green	Blue	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 blue notebooks sold = 3 u

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

7 u = 420

1 u = 420 ÷ 7 = 60

Total number of notebooks sold
= 10 u
= 10 x 60
= 600

(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 green = 80%
Percent of the notebooks left unsold that were blue = 100% - 80% = 20%

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

Number of blue notebooks that Simon had at first
= 2 u + 3 u
= 5 u
= 5 x 60
= 300

Answer(s): (a) 600; (b) 300