<PRE><B>Question 309889</B>
You must add their rates of pumping to get the rate
of pumping together
In words, the rate is:
 (1 tank)/(time to fill 1 tank)
pipe A:
{{{1/1}}} 1 tank/1 hr
pipe B:
{{{1/x}}} 1 tank/x hrs
A and B together:
{{{1/1 + 1/x = 1/.75}}}
{{{.75x + .75 = x}}}
{{{.25x = .75}}}
{{{x = 3}}}
Using pipe B alone, it takes 3 hrs to fill the tank
check:
{{{1 + 1/3 = 1/.75}}}
{{{4/3 = 4/3}}}
OK</PRE>