Answer:
100 boys at the concert
Step-by-step explanation:
At a country concert, the ratio of the number of boys to girls is 2:7
Let 'b' be the number of boys in the concert
there are 250 more girls than boys
so b+250 are the number of girls in the concert
the ratio of boys to girls is b: b+250
Now make a proportion using the ratio

Now solve for b . cross multiply the fraction


Subtract 2b from both sides

Divide both sides by 5
b=100
So there are 100 boys at the concert