Answer:
There are 30 girls at the party.
Explanation:
20 / 2 = 10
10*3 = 30
You divide the 20 boys at the party from the "every 2 boys", and you should get 10.
You then multiply the 10 by 3, for the 3 girls at the party and you should get 30 as an answer, so therefore you should get 30 as your answer.