The number of girls to the number of boys in Primary 5 Peace was 1 : 4. The number of girls to the number of boys in Primary 5 Love was 3 : 4. Both classes had the same number of girls. When 54 boys from Primary 5 Peace joined Primary 5 Love, the ratio of the number of girls to the number of boys in Primary 5 Peace became 1 : 2. Find the total enrolment of both classes.

Primary 5 Peace		Primary 5 Love
Girls	Boys	Girls	Boys
1x3	4x3	3x1	4x1
1x3		1x3
3 u	12 u	3 u	4 u

The number of girls in both classes is the same.  Make the number of girls the same.  LCM of 1 and 3 is 3.

	Primary 5 Peace		Primary 5 Love
	Girls	Boys	Girls	Boys
Before	3 u	12 u	3 u	4 u
Change		- 54		+ 54
After	1x3 = 3 u	2x3 = 6 u	3 u	4 u + 54

The number of girls in Primary 5 Peace remains unchanged.  Make the number of girls in Primary 5 the same.  LCM of 3 and 1 is 3.

Number of boys from Primary 5 Peace that joined Primary 5 Love
= 12 u - 6 u
= 6 u

6 u = 54

1 u = 54 ÷ 6 = 9

Total enrolment of both classes
= 3 u + 12 u + 3 u + 4 u
= 22 u
= 22 x 9
= 198

Answer(s): 198