Answer:
We can setup an equation for this.
Boys to Girls = 2:7
Boys = x
Girls = 250+x
Setup the ratio
x:(250+x) = 2:7
x / (250+x) = 2/7
7x = 500+2x
7x-2x = 500
x = 500/5 =100
There are 100 boys at the concert
Hope this helps:)
