The ratio of the girls to the boys in a school was 7 : 4. After 20 girls went home and 15 new boys came, there were 7 more girls than boys in the end. Find the number of students in the school at first.
| |
Girls
(1) |
Boys
(2) |
(3) |
| Before |
7 u |
4 u |
4 u |
| Change |
- 20 |
+ 15 |
+ 15 + 7 = + 22 |
| After |
7 u |
4 u + 15 |
4 u + 22 |
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)
7 u - 20 = 4 u + 22
7 u - 4 u = 22 + 20
3 u = 42
1 u = 42 ÷ 3 = 14
Number of students at first
= 7 u + 4 u
= 11 u
= 11 x 14
= 154
Answer(s): 154
