PSLE
Bobby had red notebooks and gold notebooks for sale. He sold 140 red notebooks. 30% of the notebooks sold were gold.

1. How many red notebooks and gold notebooks did Bobby sell altogether?
2. He sold 50% of his notebooks. 75% of the notebooks left unsold were red. How many gold notebooks did Bobby have at first?

	Red	Gold	Total	Total in percent
Before	14.5 u	5.5 u	20 u	100%
Change	- 70% - 7 u	- 30% - 3 u	- 100% - 10 u	- 50%
After	75% 7.5 u	25% 2.5 u	100% 10 u	50%

30% = ³⁰₁₀₀ = ³₁₀

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

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

7 u = 140

1 u = 140 ÷ 7 = 20

Total number of notebooks sold
= 10 u
= 10 x 20
= 200

(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 red = 75%
Percent of the notebooks left unsold that were gold = 100% - 75% = 25%

Number of the notebooks left unsold that were gold
= 25% x 10 u
= ²⁵₁₀₀ x 10 u
= 2.5 u

Number of gold notebooks that Bobby had at first
= 2.5 u + 3 u
= 5.5 u
= 5.5 x 20
= 110

Answer(s): (a) 200; (b) 110