PSLE
In a school, 30% of the members in Singing Club and 40% of the members in Dancing Club are boys. Both clubs have the same number of girls. The Dancing Club has 30 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	3x3	7x3	2x7	3x7
Comparing the girls in 2 clubs		1		1
	9 u	21 u	14 u	21 u

30% = ³⁰₁₀₀ = ³₁₀

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

40% = ⁴⁰₁₀₀ = ²₅

Fraction of the members in Dancing club that are girls
= 1 - ²₅
= ³₅

The number of girls in both clubs is the same. Make the numerators the same. LCM of 7 and 3 is 21. 

7x310x3 of the members in Singing Club = 3x75x7 of the members in Dancing Club
2130of the members in Singing Club = 2135 of the members in Dancing Club

Number of more boys in Dancing Club than Singing Club
= 14 u - 9 u
= 5 u

5 u = 30

1 u = 30 ÷ 5 = 6

Total number of boys
= 9 u + 14 u
= 23 u
= 23 x 6
= 138

Answer(s): 138