The number of boys to the number of girls in Primary 4 Goodness was 1 : 4. The number of boys to the number of girls in Primary 4 Peace was 3 : 5. Both classes had the same number of boys. When 15 girls from Primary 4 Goodness joined Primary 4 Peace, the ratio of the number of boys to the number of girls in Primary 4 Goodness became 1 : 3. Find the total enrolment of both classes.
Primary 4 Goodness |
Primary 4 Peace |
Boys |
Girls |
Boys |
Girls |
1x3 |
4x3 |
3x1 |
5x1 |
1x3 |
|
1x3 |
|
3 u |
12 u |
3 u |
5 u |
The number of boys in both classes is the same. Make the number of boys the same. LCM of 1 and 3 is 3.
|
Primary 4 Goodness |
Primary 4 Peace |
|
Boys |
Girls |
Boys |
Girls |
Before |
3 u |
12 u |
3 u |
5 u |
Change |
|
- 15 |
|
+ 15 |
After |
1x3 = 3 u |
3x3 = 9 u |
3 u |
5 u + 15 |
The number of boys in Primary 4 Goodness remains unchanged. Make the number of boys in Primary 4 the same. LCM of 3 and 1 is 3.
Number of girls from Primary 4 Goodness that joined Primary 4 Peace
= 12 u - 9 u
= 3 u
3 u = 15
1 u = 15 ÷ 3 = 5
Total enrolment of both classes
= 3 u + 12 u + 3 u + 5 u
= 23 u
= 23 x 5
= 115
Answer(s): 115