A can empty the tank in 28 hrs, B can fill the tank in 14 hrs, and C takes 7 hrs for filling.
If all three pipes are opened simultaneously ,how long it will take to fill the tank?  Pick.
A) 4 hr 36 minutes  B) 5 hr 36 minutes  C) 6 hr 36 minutes  D) 7 hr 36 minutes  E) None of these
Solution:time taken=(28*14*7*)/(28*14 - 14*7 + 28*7)   To solve this quicker find out LCM(28,14,7)   we get 28   Time taken =28/(-28/28 +28/14 + 28/7)   =28/(-1+2+4)   =28/5= 
<gadget id="calculator">28/5</gadget>
<output>28/5 = around 5.6</output>
5.6 hrs=5 hr 36 minutes   Answer 5 hr 36 minutes
<result>B</result>
A can empty the tank in 28 hrs, B can fill the tank in 14 hrs, and C takes 7 hrs for filling.
If all three pipes are opened simultaneously ,how long it will take to fill the tank?