Barry stands on his head for 10 minutes at a time, but then he must sit for 5 minutes before he can take another turn standing on his head.  How many turns can Barry take standing on his head during a single 2-hour period?
Each turn Barry takes standing on his head lasts for 10+5=<<10+5=15>>15 minutes.
2 hours is 60*2=<<2*60=120>>120 minutes.
Barry can take 120/15=<<120/15=8>>8 turns standing on his head over two hours.
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