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 : 5. The ratio of the number of boys to girls in Group B is 7 : 1. There are 2 times as many pupils in Group B as in Group A. There are 210 more boys in Group B than Group A. What is the total number of pupils?

Group A		Group B
12 u		8x3 = 24 u
Boys	Girls	Boys	Girls
7 u	5 u	7x3 = 21 u	1x3 = 3 u

Total number of pupils in Group A
= 7 u + 5 u
= 12 u

Total number of pupils in Group B
= 2 x 12 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 8 is 24.

Number of more boys in Group B than Group A
= 21 u - 7 u
= 14 u

14 u = 210

1 u = 210 ÷ 14 = 15

Total number of pupils
= 7 u + 5 u + 21 u + 3 u
= 36 u
= 36 x 15
= 540

Answer(s): 540