The number of boys to the number of girls in Primary 2 Joy was 2 : 5. The number of boys to the number of girls in Primary 2 Goodness was 3 : 5. Both classes had the same number of boys. When 18 girls from Primary 2 Joy joined Primary 2 Goodness, the ratio of the number of boys to the number of girls in Primary 2 Joy became 2 : 3. Find the total enrolment of both classes.
| Primary 2 Joy |
Primary 2 Goodness |
| Boys |
Girls |
Boys |
Girls |
| 2x3 |
5x3 |
3x2 |
5x2 |
| 1x6 |
|
1x6 |
|
| 6 u |
15 u |
6 u |
10 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 2 Joy |
Primary 2 Goodness |
| |
Boys |
Girls |
Boys |
Girls |
| Before |
6 u |
15 u |
6 u |
10 u |
| Change |
|
- 18 |
|
+ 18 |
| After |
2x3 =
6 u |
3x3 =
9 u |
6 u |
10 u + 18 |
The number of boys in Primary 2 Joy remains unchanged. Make the number of boys in Primary 2 the same. LCM of 6 and 2 is 6.
Number of girls from Primary 2 Joy that joined Primary 2 Goodness
= 15 u - 9 u
= 6 u
6 u = 18
1 u = 18 ÷ 6 = 3
Total enrolment of both classes
= 6 u + 15 u + 6 u + 10 u
= 37 u
= 37 x 3
= 111
Answer(s): 111
