Three taps A,B and C can fill a tank in 12,15 and 20. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in?	Choose the correct choice from the following answers.
A) 5hours  B) 7hours  C) 6hours  D) 8hours  E) 10hours
A+7hours 1 hour work = 1/12 + 1/15 = 9/60 = 3/20   A+C 1 hour work = 1/12 + 1/20  +  1= 
<gadget id="calculator"> +  1</gadget>
<output>1</output>
1/12 + 1/20= 8/60 = 2/15   Part filled in 2 hours = 3/20 + 2/15 = 17/60   Part filled in 6 hours = 3* 17/60 = 17/20   Remaining part = 1 - 17/20 = 3/20   Now it is the turn of A and 7hours and 3/20 part is filled by A and 7hours in 1hour   Total time taken to fill the tank = 6+1= 
<gadget id="calculator">6+1</gadget>
<output>7</output>
7 hours   Answer is 7hours
<result>B</result>
Three taps A,B and C can fill a tank in 12,15 and 20. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in?