question: Chris has a two-speed lawn mower. He can mow his entire lawn in "turtle" mode in 1 hour, or 40 minutes in "rabbit" mode. Today, he experimented by mowing half in turtle mode and half in rabbit mode. How many minutes did it take him to mow the lawn?
answer: He spends 60/2=<<60/2=30>>30 minutes in turtle mode
  He spends 40/2=<<40/2=20>>20 minutes in rabbit mode
  He took 30+20=<<30+20=50>>50 minutes to mow the lawn.
  #### 50