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 [tex] \frac{1}{4} [/tex] of the job.
The finished job = [tex] \dfrac{\text{time of work}}{\text{time needed to do whole job}} [/tex]
The finished job = [tex] \dfrac{\text{1 hour}}{\text{4 hours}} [/tex]
The finished job = [tex] \dfrac{1}{4} [/tex]
Determine part of the remaining job
remaining job = 1 - the finished job
remaining job = 1 - [tex] \frac{1}{4} [/tex]
remaining job = [tex] \frac{3}{4} [/tex]
The remaining job for the son is 3/4 of the job
Determine time needed to do 3/4 of the job
time needed = [tex] \frac{3}{4} \times \text{time needed to do whole job}[/tex]
time needed = [tex] \frac{3}{4} \times 3[/tex]
time needed = [tex] \frac{9}{4}[/tex]
time needed = [tex]2 \frac{1}{4} [/tex] hours
time needed = 2 hours + 15 minutes
To finish mowing the lawn, the son needs 2 hours and 15 minutes
