Question 1147442
new pump time, x
old pump time, 4x
both together  4


{{{1/4x+1/x=1/4}}}

{{{4x(1/4x+1/4)=4x(1/4)}}}

{{{1+4=x}}}

{{{x=5}}}

{{{4x=highlight(20)}}} hours of time for old pump by itself