其它
A certain play has two $$45$$-minute parts and an intermission between them. The play started at $$10:50$$ and ended at $$12:40$$. How many minutes long was the intermission? 
Overseas Competition->Knowledge Point->Combinatorics->Time Problem
From $$10:50$$ to $$12:40$$ = $$1$$ h $$50$$ min, $$1$$ h $$50$$ min = $$110$$ min, two $$45$$-minute parts = $$90$$ min, and $$110 - 90 = 20$$ min. 