PSLE
The pupils at a school choir are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 7 : 2. The ratio of the number of boys to girls in Group B is 5 : 1. There are 2 times as many pupils in Group B as in Group A. There are 16 more boys in Group B than Group A. What is the total number of girls?

Group A		Group B
9 u		6x3 = 18 u
Boys	Girls	Boys	Girls
7 u	2 u	5x3 = 15 u	1x3 = 3 u

Total number of pupils in Group A
= 7 u + 2 u
= 9 u

Total number of pupils in Group B
= 2 x 9 u
= 18 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 18 and 6 is 18.

Number of more boys in Group B than Group A
= 15 u - 7 u
= 8 u

8 u = 16

1 u = 16 ÷ 8 = 2

Total number of girls
= 2 u + 3 u
= 5 u
= 5 x 2
= 10

Answer(s): 10