PSLE
The pupils at a camp are divided in Team A and Team B. The ratio of the number of girls to boys in Team A is 4 : 1. The ratio of the number of girls to boys in Team B is 7 : 3. There are 4 times as many pupils in Team B as in Team A. There are 90 more girls in Team B than Team A. What is the total number of boys?

Team A		Team B
5 u		10x2 = 20 u
Girls	Boys	Girls	Boys
4 u	1 u	7x2 = 14 u	3x2 = 6 u

Total number of pupils in Team A
= 4 u + 1 u
= 5 u

Total number of pupils in Team B
= 4 x 5 u
= 20 u

The total number of pupils in Team B is repeated.
Use LCM to make the total number of pupils in Team B the same.
LCM of 20 and 10 is 20.

Number of more girls in Team B than Team A
= 14 u - 4 u
= 10 u

10 u = 90

1 u = 90 ÷ 10 = 9

Total number of boys
= 1 u + 6 u
= 7 u
= 7 x 9
= 63

Answer(s): 63