PSLE
The students at a sports meet are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 3 : 2. The ratio of the number of boys to girls in Group B is 9 : 1. There are 4 times as many students in Group B as in Group A. There are 45 more boys in Group B than Group A. What is the total number of students?

Group A		Group B
5 u		10x2 = 20 u
Boys	Girls	Boys	Girls
3 u	2 u	9x2 = 18 u	1x2 = 2 u

Total number of students in Group A
= 3 u + 2 u
= 5 u

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

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

Number of more boys in Group B than Group A
= 18 u - 3 u
= 15 u

15 u = 45

1 u = 45 ÷ 15 = 3

Total number of students
= 3 u + 2 u + 18 u + 2 u
= 25 u
= 25 x 3
= 75

Answer(s): 75