The number of boys to the number of girls in Primary 1 Peace was 2 : 5. The number of boys to the number of girls in Primary 1 Faithfulness was 3 : 4. Both classes had the same number of boys. When 24 girls from Primary 1 Peace joined Primary 1 Faithfulness, the ratio of the number of boys to the number of girls in Primary 1 Peace became 2 : 3. Find the total enrolment of both classes.

Primary 1 Peace		Primary 1 Faithfulness
Boys	Girls	Boys	Girls
2x3	5x3	3x2	4x2
1x6		1x6
6 u	15 u	6 u	8 u

The number of boys in both classes is the same.  Make the number of boys the same.  LCM of 2 and 3 is 6.

	Primary 1 Peace		Primary 1 Faithfulness
	Boys	Girls	Boys	Girls
Before	6 u	15 u	6 u	8 u
Change		- 24		+ 24
After	2x3 = 6 u	3x3 = 9 u	6 u	8 u + 24

The number of boys in Primary 1 Peace remains unchanged.  Make the number of boys in Primary 1 the same.  LCM of 6 and 2 is 6.

Number of girls from Primary 1 Peace that joined Primary 1 Faithfulness
= 15 u - 9 u
= 6 u

6 u = 24

1 u = 24 ÷ 6 = 4

Total enrolment of both classes
= 6 u + 15 u + 6 u + 8 u
= 35 u
= 35 x 4
= 140

Answer(s): 140