Math CentralQuandaries & Queries


Question from kevin, a student:

I need help setting up a equation to solve the following question: If a gardener can mow 3 lawns in 7 hours, how long should it take him to mow 17 lawns. I can solve the problem, but I don't know how to set up the equation.

Hi Kevin,

This is a rate problem and I know I have to use the rate at which the gardner mows the lawn but I don't know whether to express the rate as lawns per hour or hours per lawn. I let the units tell me what to do.

I want an answer in hours when he mows 17 lawns so my equation is going to look like

rate times number of lawns equals number of hours, or

equation 1

Thus, in order for the units to cancel I need the rate in hours per lawn

equation 2

This is then my equation which yields

equation 3

I hope this helps,

About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS