The number of girls to the number of boys in Primary 5 Love was 1 : 4. The number of girls to the number of boys in Primary 5 Joy was 4 : 5. Both classes had the same number of girls. When 30 boys from Primary 5 Love joined Primary 5 Joy, the ratio of the number of girls to the number of boys in Primary 5 Love became 2 : 3. Find the total enrolment of both classes.
Primary 5 Love |
Primary 5 Joy |
Girls |
Boys |
Girls |
Boys |
1x4 |
4x4 |
4x1 |
5x1 |
1x4 |
|
1x4 |
|
4 u |
16 u |
4 u |
5 u |
The number of girls in both classes is the same. Make the number of girls the same. LCM of 1 and 4 is 4.
|
Primary 5 Love |
Primary 5 Joy |
|
Girls |
Boys |
Girls |
Boys |
Before |
4 u |
16 u |
4 u |
5 u |
Change |
|
- 30 |
|
+ 30 |
After |
2x2 = 4 u |
3x2 = 6 u |
4 u |
5 u + 30 |
The number of girls in Primary 5 Love remains unchanged. Make the number of girls in Primary 5 the same. LCM of 4 and 2 is 4.
Number of boys from Primary 5 Love that joined Primary 5 Joy
= 16 u - 6 u
= 10 u
10 u = 30
1 u = 30 ÷ 10 = 3
Total enrolment of both classes
= 4 u + 16 u + 4 u + 5 u
= 29 u
= 29 x 3
= 87
Answer(s): 87