Question 133977
If it takes Bob 3 hours to mow a lawn, then he can mow {{{1/3}}} of a lawn per hour.  Likewise, John can mow {{{1/2}}} of a lawn per hour.  Together they can mow {{{1/3+1/2=5/6}}} of a lawn per hour.  So it will take {{{1/(5/6)=6/5}}} hours for them to mow one lawn together.  {{{6/5}}} hour is 1 and 1/5 hour is 1 hour and 12 minutes.  An hour and a quarter if you give them a glass of lemonade when they are done.