PSLE
The pupils at a school choir are divided in Group A and Group B. The ratio of the number of girls to boys in Group A is 3 : 1. The ratio of the number of girls to boys in Group B is 7 : 3. There are 5 times as many pupils in Group B as in Group A. There are 66 more girls in Group B than Group A. What is the total number of pupils?

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

Total number of pupils in Group A
= 3 u + 1 u
= 4 u

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

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

Number of more girls in Group B than Group A
= 14 u - 3 u
= 11 u

11 u = 66

1 u = 66 ÷ 11 = 6

Total number of pupils
= 3 u + 1 u + 14 u + 6 u
= 24 u
= 24 x 6
= 144

Answer(s): 144