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=<T>add(10, 5)=15 minutes.
2 hours is 60*2=<T>multiply(2, 60)=120 minutes.
Barry can take 120/15=<T>divide(120, 15)=8.0 turns standing on his head over two hours.
