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A certain play has two $30$-minute parts and one intermission among them. The play started at $8:00$ and ended at $9:15$. How many minutes long were the intermission? (Adapted from 2010 Math Kangaroo Problem, Level 1-2, Question \#19) 
Overseas Competition->Knowledge Point->Combinatorics->Time Problem
From $8:00$ to $9:15$ = $1$ h $15$ min, $1$ h $15$ min = $75$ min, two $30$-minute parts = $60$ min, $75 - 60$ = $15$ min. 