Two pipes a and b can fill a tank in 12 hours and 15 hours respectively.if both pipe open together in tank,then how much time it take to fill the tank?  Choose the most appropriate option.
A) 15	B) 18	C) 20/3	D) 19/4	E) 25/4
in 1 hour pipe a fill=1/12   in 1 hour pipe b fill=1/15   pipe(a+b) in 1 hour=[1/12+1/15]=3/20   total time taken to fill the tank=20/3 hour   answer 20/3
<result>C</result>
Two pipes a and b can fill a tank in 12 hours and 15 hours respectively.if both pipe open together in tank,then how much time it take to fill the tank?