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 7 : 1. The ratio of the number of girls to boys in Group B is 11 : 1. There are 3 times as many pupils in Group B as in Group A. There are 120 more girls in Group B than Group A. What is the total number of pupils?

Group A		Group B
8 u		12x2 = 24 u
Girls	Boys	Girls	Boys
7 u	1 u	11x2 = 22 u	1x2 = 2 u

Total number of pupils in Group A
= 7 u + 1 u
= 8 u

Total number of pupils in Group B
= 3 x 8 u
= 24 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 24 and 12 is 24.

Number of more girls in Group B than Group A
= 22 u - 7 u
= 15 u

15 u = 120

1 u = 120 ÷ 15 = 8

Total number of pupils
= 7 u + 1 u + 22 u + 2 u
= 32 u
= 32 x 8
= 256

Answer(s): 256