At first, there were 396 more boys than girls at the concert hall. By 4 p.m., a total of 258 boys and girls left the concert hall. There were as many boys as girls who left the concert hall. In the end, there were 4 times as many boys as girls who remained behind. How many boys were at the concert hall at first?
|
Boys |
Girls |
Difference |
Before |
4 u + 129 |
1 u + 129 |
396 |
Change |
- 129 |
- 129 |
|
After |
4 u |
1 u |
3 u |
Since there was the same number of girls and boys that left, the difference between the number of girls and boys remains unchanged.
3 u = 396
1 u = 396 ÷ 3 = 132
Number of boys in the end
= 4 u
= 4 x 132
= 528
Number of boys that left
= 258 ÷ 2
= 129
Number of boys at first
= 528 + 129
= 657
Answer(s): 657