The number of boys to the number of girls in Primary 2 Kindness was 1 : 4. The number of boys to the number of girls in Primary 2 Patience was 4 : 5. Both classes had the same number of boys. When 20 girls from Primary 2 Kindness joined Primary 2 Patience, the ratio of the number of boys to the number of girls in Primary 2 Kindness became 1 : 3. Find the total enrolment of both classes.
Primary 2 Kindness |
Primary 2 Patience |
Boys |
Girls |
Boys |
Girls |
1x4 |
4x4 |
4x1 |
5x1 |
1x4 |
|
1x4 |
|
4 u |
16 u |
4 u |
5 u |
The number of boys in both classes is the same. Make the number of boys the same. LCM of 1 and 4 is 4.
|
Primary 2 Kindness |
Primary 2 Patience |
|
Boys |
Girls |
Boys |
Girls |
Before |
4 u |
16 u |
4 u |
5 u |
Change |
|
- 20 |
|
+ 20 |
After |
1x4 = 4 u |
3x4 = 12 u |
4 u |
5 u + 20 |
The number of boys in Primary 2 Kindness remains unchanged. Make the number of boys in Primary 2 the same. LCM of 4 and 1 is 4.
Number of girls from Primary 2 Kindness that joined Primary 2 Patience
= 16 u - 12 u
= 4 u
4 u = 20
1 u = 20 ÷ 4 = 5
Total enrolment of both classes
= 4 u + 16 u + 4 u + 5 u
= 29 u
= 29 x 5
= 145
Answer(s): 145