The number of boys to the number of girls in Primary 5 Patience was 2 : 5. The number of boys to the number of girls in Primary 5 Faithfulness was 5 : 6. Both classes had the same number of boys. When 22 girls from Primary 5 Patience joined Primary 5 Faithfulness, the ratio of the number of boys to the number of girls in Primary 5 Patience became 5 : 7. Find the total enrolment of both classes.

Primary 5 Patience		Primary 5 Faithfulness
Boys	Girls	Boys	Girls
2x5	5x5	5x2	6x2
1x10		1x10
10 u	25 u	10 u	12 u

The number of boys in both classes is the same.  Make the number of boys the same.  LCM of 2 and 5 is 10.

	Primary 5 Patience		Primary 5 Faithfulness
	Boys	Girls	Boys	Girls
Before	10 u	25 u	10 u	12 u
Change		- 22		+ 22
After	5x2 = 10 u	7x2 = 14 u	10 u	12 u + 22

The number of boys in Primary 5 Patience remains unchanged.  Make the number of boys in Primary 5 the same.  LCM of 10 and 5 is 10.

Number of girls from Primary 5 Patience that joined Primary 5 Faithfulness
= 25 u - 14 u
= 11 u

11 u = 22

1 u = 22 ÷ 11 = 2

Total enrolment of both classes
= 10 u + 25 u + 10 u + 12 u
= 57 u
= 57 x 2
= 114

Answer(s): 114