Question 846135
Are the pumps congruent?  Find the rate for one pump.  The rates of pumps operating at the same time are simply additive.  This is a uniform rates problem so you want the rate of the pumping, based on the rate for one pump.  


R*t=j ______________ and  j for job, being "fill the pool".


4 pumps____________{{{1/24}}}  jobs per hour
1 pump_____________{{{(1/(4*24))=1/96}}} jobs per hour which is four times slower, which should intuitively make sense.


You have some unknown n pumps and you want t=8 hours.
{{{highlight(n(1/96)*8=1)}}};
Solve for n.