Question 310430
a filler pipe can fill a tank in 10 hours, while an outlet pipe can empty the
 tank in 15 hours. how long will it take to fill the empty tank with both pipes operating 
:
Let t = time required when both pipes are on
:
Let the completed job = 1 (a full tank)
:
Fill is +, drain is -
:
{{{t/10}}} - {{{t/15}}} = 1
Multiply eq by 30,
30*{{{t/10}}} - 30*{{{t/15}}} = 30(1)
 results
3t - 2t = 30
t = 30 hrs to fill with both pipes on