The number of boys to the number of girls in Primary 4 Patience was 1 : 4. The number of boys to the number of girls in Primary 4 Peace was 3 : 4. Both classes had the same number of boys. When 24 girls from Primary 4 Patience joined Primary 4 Peace, the ratio of the number of boys to the number of girls in Primary 4 Patience became 1 : 2. Find the total enrolment of both classes.

Primary 4 Patience		Primary 4 Peace
Boys	Girls	Boys	Girls
1x3	4x3	3x1	4x1
1x3		1x3
3 u	12 u	3 u	4 u

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

	Primary 4 Patience		Primary 4 Peace
	Boys	Girls	Boys	Girls
Before	3 u	12 u	3 u	4 u
Change		- 24		+ 24
After	1x3 = 3 u	2x3 = 6 u	3 u	4 u + 24

The number of boys in Primary 4 Patience remains unchanged.  Make the number of boys in Primary 4 the same.  LCM of 3 and 1 is 3.

Number of girls from Primary 4 Patience that joined Primary 4 Peace
= 12 u - 6 u
= 6 u

6 u = 24

1 u = 24 ÷ 6 = 4

Total enrolment of both classes
= 3 u + 12 u + 3 u + 4 u
= 22 u
= 22 x 4
= 88

Answer(s): 88