PSLE
In a school, 30% of the members in Computer Club and 60% of the members in Art Club are boys. Both clubs have the same number of girls. The Art Club has 30 more boys than the Computer Club. How many boys are there altogether?

	Computer Club		Art Club
Types	Boys	Girls	Boys	Girls
Comparing the boys and the girls in each club	3x2	7x2	3x7	2x7
Comparing the girls in 2 clubs		1		1
	6 u	14 u	21 u	14 u

30% = ³⁰₁₀₀ = ³₁₀

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

60% = ⁶⁰₁₀₀ = ³₅

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

The number of girls in both clubs is the same. Make the numerators the same. LCM of 7 and 2 is 14. 

7x210x2 of the members in Computer Club = 2x75x7 of the members in Art Club
1420of the members in Computer Club = 1435 of the members in Art Club

Number of more boys in Art Club than Computer Club
= 21 u - 6 u
= 15 u

15 u = 30

1 u = 30 ÷ 15 = 2

Total number of boys
= 6 u + 21 u
= 27 u
= 27 x 2
= 54

Answer(s): 54