PSLE
Gabriel had silver notebooks and yellow notebooks for sale. He sold 120 silver notebooks. 70% of the notebooks sold were yellow.

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

	Silver	Yellow	Total	Total in percent
Before	9 u	11 u	20 u	100%
Change	- 30% - 3 u	- 70% - 7 u	- 100% - 10 u	- 50%
After	60% 6 u	40% 4 u	100% 10 u	50%

70% = ⁷⁰₁₀₀ = ⁷₁₀

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

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

3 u = 120

1 u = 120 ÷ 3 = 40

Total number of notebooks sold
= 10 u
= 10 x 40
= 400

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

Number of the notebooks left unsold that were yellow
= 40% x 10 u
= ⁴⁰₁₀₀ x 10 u
= 4 u

Number of yellow notebooks that Gabriel had at first
= 4 u + 7 u
= 11 u
= 11 x 40
= 440

Answer(s): (a) 400; (b) 440