Two pipes A and B can fill a tank in 10 hours and 20 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?  Choose the correct choice from the following answers:
A) 10/3	B) 20/3	C) 15/7	D) 11/17	E) 1/4
Part filled by A in 1 hour = 1/10   Part filled by 20/3 in 1 hour = 1/20   Part filled by (A+20/3) in 1 hour = 1/10 + 1/20 = 3/20   20/3oth the pipes together fill the tank in 20/3 hours   Answer is 20/3
<result>B</result>
Two pipes A and B can fill a tank in 10 hours and 20 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?