The number of girls to the number of boys in Primary 2 Joy was 1 : 4. The number of girls to the number of boys in Primary 2 Patience was 3 : 4. Both classes had the same number of girls. When 9 boys from Primary 2 Joy joined Primary 2 Patience, the ratio of the number of girls to the number of boys in Primary 2 Joy became 1 : 3. Find the total enrolment of both classes.
Primary 2 Joy |
Primary 2 Patience |
Girls |
Boys |
Girls |
Boys |
1x3 |
4x3 |
3x1 |
4x1 |
1x3 |
|
1x3 |
|
3 u |
12 u |
3 u |
4 u |
The number of girls in both classes is the same. Make the number of girls the same. LCM of 1 and 3 is 3.
|
Primary 2 Joy |
Primary 2 Patience |
|
Girls |
Boys |
Girls |
Boys |
Before |
3 u |
12 u |
3 u |
4 u |
Change |
|
- 9 |
|
+ 9 |
After |
1x3 = 3 u |
3x3 = 9 u |
3 u |
4 u + 9 |
The number of girls in Primary 2 Joy remains unchanged. Make the number of girls in Primary 2 the same. LCM of 3 and 1 is 3.
Number of boys from Primary 2 Joy that joined Primary 2 Patience
= 12 u - 9 u
= 3 u
3 u = 9
1 u = 9 ÷ 3 = 3
Total enrolment of both classes
= 3 u + 12 u + 3 u + 4 u
= 22 u
= 22 x 3
= 66
Answer(s): 66