Answer:
90 Couples
Explanation:
There were 250 total people at the beginning at the party. 70 people left at 11pm.
Subtract 70 from 250:
There were 180 people that stayed.
A couple consists of two people. The question asks how many couples stayed at the party, not people.
Divide 180 by 2:
There would be 90 couples that stayed at the party.