### Instruction: Mary can mow a lawn in four hours and Tom can mow the lawn in 5 hours. If Tom works for 2 hours alone, what fractional part of the lawn remains to be mowed?### Response: I want to find out how much of the lawn Tom can mow in 2 hours, and then subtract that from the total lawn area.
To do that, I need to know the rate at which Tom mows the lawn, which is the inverse of the time he takes to mow the whole lawn.
So Tom's rate is 1/5 lawn per hour, or 0.2 lawn per hour.
That means in 2 hours, Tom can mow 2 * 0.2 = 0.4 of the lawn.