Tap 'A' can fill the tank completely in 4 hrs while tap 'B' can empty it by 8 hrs. By mistake, the person forgot to close the tap 'B', As a result, both the tapes, remained open. After 4 hrs, the person realized the mistake and immediately closed the tap 'B'. In how much time now onward, would the tank be full?	Choose the most appropriate option.
A) 2
B) 3
C) 1/2
D) 1/4
E) 5
Explanation :   Rate of filling tap A = 1/4 per hr   Rate of emptying of tap B = 1/8 per hr   When both the taps remain open, the effective rate of filling   = 1/4 - 1/8 = 1/8 of the tank   Hence in 4 hr, the tank must have been full to the   Extent of 4 x 1/8 = 1/2 Capacity   Remaining volume = 1/2 capacity   Now emptying tap is closed rate of filling would be 1/4 per hr   Time reqd. to fill = Empty volume/Filling rate   = (1/2)/(1/4)= 
<gadget id="calculator">(1/2)/(1/4)</gadget>
<output>2</output>
2 hrs   2nswer : 2
<result>A</result>
Tap 'A' can fill the tank completely in 4 hrs while tap 'B' can empty it by 8 hrs. By mistake, the person forgot to close the tap 'B', As a result, both the tapes, remained open. After 4 hrs, the person realized the mistake and immediately closed the tap 'B'. In how much time now onward, would the tank be full?