The number of boys to the number of girls in Primary 6 Faithfulness was 1 : 4. The number of boys to the number of girls in Primary 6 Peace was 3 : 4. Both classes had the same number of boys. When 36 girls from Primary 6 Faithfulness joined Primary 6 Peace, the ratio of the number of boys to the number of girls in Primary 6 Faithfulness became 1 : 2. Find the total enrolment of both classes.

Primary 6 Faithfulness		Primary 6 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 6 Faithfulness		Primary 6 Peace
	Boys	Girls	Boys	Girls
Before	3 u	12 u	3 u	4 u
Change		- 36		+ 36
After	1x3 = 3 u	2x3 = 6 u	3 u	4 u + 36

The number of boys in Primary 6 Faithfulness remains unchanged.  Make the number of boys in Primary 6 the same.  LCM of 3 and 1 is 3.

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

6 u = 36

1 u = 36 ÷ 6 = 6

Total enrolment of both classes
= 3 u + 12 u + 3 u + 4 u
= 22 u
= 22 x 6
= 132

Answer(s): 132