The number of boys to the number of girls in Primary 6 Faithfulness was 2 : 5. The number of boys to the number of girls in Primary 6 Peace was 5 : 6. Both classes had the same number of boys. When 18 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 5 : 8. Find the total enrolment of both classes.
| Primary 6 Faithfulness |
Primary 6 Peace |
| 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 6 Faithfulness |
Primary 6 Peace |
| |
Boys |
Girls |
Boys |
Girls |
| Before |
10 u |
25 u |
10 u |
12 u |
| Change |
|
- 18 |
|
+ 18 |
| After |
5x2 =
10 u |
8x2 =
16 u |
10 u |
12 u + 18 |
The number of boys in Primary 6 Faithfulness remains unchanged. Make the number of boys in Primary 6 the same. LCM of 10 and 5 is 10.
Number of girls from Primary 6 Faithfulness that joined Primary 6 Peace
= 25 u - 16 u
= 9 u
9 u = 18
1 u = 18 ÷ 9 = 2
Total enrolment of both classes
= 10 u + 25 u + 10 u + 12 u
= 57 u
= 57 x 2
= 114
Answer(s): 114
