At first, there were 420 more girls than boys at the museum. By 3 p.m., a total of 278 girls and boys left the museum. There were as many girls as boys who left the museum. In the end, there were 4 times as many girls as boys who remained behind. How many girls were at the museum at first?
| |
Girls |
Boys |
Difference |
| Before |
4 u + 139 |
1 u + 139 |
420 |
| Change |
- 139 |
- 139 |
|
| After |
4 u |
1 u |
3 u |
Since there was the same number of boys and girls that left, the difference between the number of boys and girls remains unchanged.
3 u = 420
1 u = 420 ÷ 3 = 140
Number of girls in the end
= 4 u
= 4 x 140
= 560
Number of girls that left
= 278 ÷ 2
= 139
Number of girls at first
= 560 + 139
= 699
Answer(s): 699
