Two pipes A and B can fill a tank in 30 and 40 minutes respectively. If both the pipes are used together, then how long it will take to fill the tank ?
Select
A) 16 1/7
B) 17 1/7 mins.
C) 15 1/7
D) 14 1/7
E) 18 1/7
Explanation:   In this type of questions we first get the filling in 1 minute for both pipes then we will add them to get the result, as   Part filled by A in 1 min = 1/30   Part filled by B in 1 min = 1/40   Part filled by (A+B) in 1 min = 1/30 + 1/40   = 7/120   So both pipes can fill the tank in 17 1/7 mins.   Option 17 1/7 mins.
<result>B</result>
Two pipes A and B can fill a tank in 30 and 40 minutes respectively. If both the pipes are used together, then how long it will take to fill the tank ?