PSLE
Ben had green notebooks and gold notebooks for sale. He sold 330 green notebooks. 70% of the notebooks sold were gold.

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

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

70% = ⁷⁰₁₀₀ = ⁷₁₀

Total number of notebooks sold = 10 u
Number of gold notebooks sold = 7 u

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

3 u = 330

1 u = 330 ÷ 3 = 110

Total number of notebooks sold
= 10 u
= 10 x 110
= 1100

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

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

Number of gold notebooks that Ben had at first
= 3 u + 7 u
= 10 u
= 10 x 110
= 1100

Answer(s): (a) 1100; (b) 1100