<PRE><B>Question 902563</B>
Tap A can fill up an empty tank in 3 hours. Tap B can fill up the same empty tank in 4 hours. Tap C can fill up the same tank in 12 hours. How long will it take to fill up the empty tank if all the taps are turned on at the same time? 


If I can do a job in 2 hour , then it means that I do 1/2 the job in 1 hour.

Similarly if a tap  A fills a tank in 3 hours
The tap will fill 1/3 of the tank in 1 hour.

Tap B takes 4 hours to fill a tank
Similarly Tap B fills 1/4 of the tank in hour

In the same way tap C fills 1/12 of the tank in 1 hour

When all taps are on

In 1 hour Tap A, tap B and tap C together fill up 1/3 + 1/4 +1/12 of the tank in hour.

1/3 + 1/4 + 1/12 

LCM of the denominator  is 12

=(4+3+1)/12

=8/12 

= 2/3 

2/3 of the tank is filled by all the taps in 1 hour
1 tank is filled in 1/(2/3) hours

= 3/2 hours

= 1.5 hours

OR 1 hour 30 minutes




</PRE>