PSLE
In a school, 70% of the members in Singing Club and 75% of the members in Dancing Club are boys. Both clubs have the same number of girls. The Dancing Club has 20 more boys than the Singing Club. How many boys are there altogether?

	Singing Club		Dancing Club
Types	Boys	Girls	Boys	Girls
Comparing the boys and the girls in each club	7x1	3x1	3x3	1x3
Comparing the girls in 2 clubs		1		1
	7 u	3 u	9 u	3 u

70% = ⁷⁰₁₀₀ = ⁷₁₀

Fraction of the members in Singing Club that are girls
= 1 - ⁷₁₀
= ³₁₀

75% = ⁷⁵₁₀₀ = ³₄

Fraction of the members in Dancing club that are girls
= 1 - ³₄
= ¹₄

The number of girls in both clubs is the same. Make the numerators the same. LCM of 3 and 1 is 3. 

3x110x1 of the members in Singing Club = 1x34x3 of the members in Dancing Club
310of the members in Singing Club = 312 of the members in Dancing Club

Number of more boys in Dancing Club than Singing Club
= 9 u - 7 u
= 2 u

2 u = 20

1 u = 20 ÷ 2 = 10

Total number of boys
= 7 u + 9 u
= 16 u
= 16 x 10
= 160

Answer(s): 160