PSLE
The pupils at a camp are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 2 : 1. The ratio of the number of boys to girls in Group B is 5 : 1. There are 4 times as many pupils in Group B as in Group A. There are 72 less boys in Group A than Group B. What is the total number of pupils in Group A?

Group A		Group B
3 u		6x2 = 12 u
Boys	Girls	Boys	Girls
2 u	1 u	5x2 = 10 u	1x2 = 2 u

Total number of pupils in Group A
= 2 u + 1 u
= 3 u

Total number of pupils in Group B
= 4 x 3 u
= 12 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 12 and 6 is 12.

Number of less boys in Group A than Group B
= 10 u - 2 u
= 8 u

8 u = 72

1 u = 72 ÷ 8 = 9

Total number of pupils in Group A
= 2 u + 1 u
= 3 u
= 3 x 9
= 27

Answer(s): 27