Question 257730
This is a typical work problem.
We have to find out how much work is done in one hour then add them
The two together has to be less than the faster alone but the slower doesn't contribute much.
In one hour the pipe can do 1/12 of the job.
The hose can do 1/30 of the job in an hour
j/12+j/30=1
lcd 60

5j/60+2j/60=7j/60
7j=60
j=60/7
j=8.57143 hours
about 8 hrs 34 minutes 17 seconds so the slower contributed 2.5 hours savings