The number of girls to the number of boys in Primary 1 Joy was 2 : 5. The number of girls to the number of boys in Primary 1 Faithfulness was 3 : 5. Both classes had the same number of girls. When 30 boys from Primary 1 Joy joined Primary 1 Faithfulness, the ratio of the number of girls to the number of boys in Primary 1 Joy became 2 : 3. Find the total enrolment of both classes.
Primary 1 Joy |
Primary 1 Faithfulness |
Girls |
Boys |
Girls |
Boys |
2x3 |
5x3 |
3x2 |
5x2 |
1x6 |
|
1x6 |
|
6 u |
15 u |
6 u |
10 u |
The number of girls in both classes is the same. Make the number of girls the same. LCM of 2 and 3 is 6.
|
Primary 1 Joy |
Primary 1 Faithfulness |
|
Girls |
Boys |
Girls |
Boys |
Before |
6 u |
15 u |
6 u |
10 u |
Change |
|
- 30 |
|
+ 30 |
After |
2x3 = 6 u |
3x3 = 9 u |
6 u |
10 u + 30 |
The number of girls in Primary 1 Joy remains unchanged. Make the number of girls in Primary 1 the same. LCM of 6 and 2 is 6.
Number of boys from Primary 1 Joy that joined Primary 1 Faithfulness
= 15 u - 9 u
= 6 u
6 u = 30
1 u = 30 ÷ 6 = 5
Total enrolment of both classes
= 6 u + 15 u + 6 u + 10 u
= 37 u
= 37 x 5
= 185
Answer(s): 185