PSLE
Ken had blue notebooks and green notebooks for sale. He sold 490 blue notebooks. 30% of the notebooks sold were green.

1. How many blue notebooks and green notebooks did Ken sell altogether?
2. He sold 50% of his notebooks. 70% of the notebooks left unsold were blue. How many green notebooks did Ken have at first?

	Blue	Green	Total	Total in percent
Before	14 u	6 u	20 u	100%
Change	- 70% - 7 u	- 30% - 3 u	- 100% - 10 u	- 50%
After	70% 7 u	30% 3 u	100% 10 u	50%

30% = ³⁰₁₀₀ = ³₁₀

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

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

7 u = 490

1 u = 490 ÷ 7 = 70

Total number of notebooks sold
= 10 u
= 10 x 70
= 700

(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 blue = 70%
Percent of the notebooks left unsold that were green = 100% - 70% = 30%

Number of the notebooks left unsold that were green
= 30% x 10 u
= ³⁰₁₀₀ x 10 u
= 3 u

Number of green notebooks that Ken had at first
= 3 u + 3 u
= 6 u
= 6 x 70
= 420

Answer(s): (a) 700; (b) 420