Two pipes A and B can fill a tank in 10hour and 15 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?  Choose the correct choice.
A) 2hrs B) 6hrs C) 5hrs D) 4hrs E) 1hr
Part filled by A in 1 hour = 1/10   part filled by B in 1 hour = 1/15   Part filled by A+B in 1 hour = 1/10 + 1/15 = 1/6   Both the pipes will together will fill the tank in 6 hours.   Answer is 6hrs
<result>B</result>
Two pipes A and B can fill a tank in 10hour and 15 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?