First man mows the lawn in 6 hours so he mows 1/6 of the lawn per hour
Second man mows at 1/4 lawn per hour
Third man mows at 1/3 lawn per hour
The total of the three: 1/6 + 1/4 + 1/3 = 2/12 + 3/12 + 4/12 = 9/12 = 3/4 of a lawn per hour.
1 lawn / 3/4 lawn per hour = 1 and 1/3 hours all together.
Answer: 1 and 1/3 hours
