Question

A man can mow his lawn in 4 hours. His son can do the job in 3 hours. If the son takes over an hour after his father, how long will it take him to finish mowing the lawn?

Answer 1

Determine part of the job that has been done by the father.
The father did for an hour before the son took over, and he could complete the job within 4 hours. That means he already did
`(1)/(4)` of the job.
The finished job =
`\frac{\text{time of work}}{\text{time needed to do whole job}}`
The finished job =
`\frac{\text{1 hour}}{\text{4 hours}}`
The finished job =
`(1)/(4)`

Determine part of the remaining job
remaining job = 1 - the finished job
remaining job = 1 -
`(1)/(4)`
remaining job =
`(3)/(4)`
The remaining job for the son is 3/4 of the job

Determine time needed to do 3/4 of the job
time needed =
`(3)/(4) * \text{time needed to do whole job}`
time needed =
`(3)/(4) * 3`
time needed =
`(9)/(4)`
time needed =
`2 (1)/(4)` hours
time needed = 2 hours + 15 minutes

To finish mowing the lawn, the son needs 2 hours and 15 minutes