<PRE><B>Question 397048</B>
Pipe A can fill a tank in 24 minutes and pipe B can fill the tank in 32 minutes.
 Both pipes are opened at the same time. After how many minutes should pipe B
be turned off so that the tank is full 20 minutes after both pipes were opened?
:
Let b = time that pipe be is turned to accomplish this
Let the completed job = 1 (a full tank)
:
{{{20/24}}} + {{{b/32}}} = 1
multiply by the LCM, 96, results:
4(20) + 3b = 96
80 + 3b = 96
3b = 96 - 80
3b = 16 
b = {{{16/3}}}
b = 5.33 min; 5 min, 20 sec 
Pipe B is turned off after 5 min 20 sec
:
:
Check this
20/24 + 5.33/32 =
.833 + .1667 = 1</PRE>