The ratio of the girls to the boys in a school was 8 : 5. After 10 girls went home and 13 new boys came, there were 7 more girls than boys in the end. Find the number of pupils in the school in the end.
| |
Girls
(1) |
Boys
(2) |
(3) |
| Before |
8 u |
5 u |
5 u |
| Change |
- 10 |
+ 13 |
+ 13 + 7 = + 20 |
| After |
8 u |
5 u + 13 |
5 u + 20 |
Comparing girls and
boys in the end |
7 more |
|
|
Since the number of girls is 7 more than the number of boys in the end, when we
add 7 to (2) to form (3), the number of girls and boys in the end will be the same.
(1) = (3)
8 u - 10 = 5 u + 20
8 u - 5 u = 20 + 10
3 u = 30
1 u = 30 ÷ 3 = 10
Number of pupils in the end
= 8 u + 5 u - 10 + 13
= 13 u + 3
= 13 x 10 + 3
= 130 + 3
= 133
Answer(s): 133
