There are two tank A and B to fill up a water tank. The

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There are two tank A and B to fill up a water tank. The tank can be filled in 40 min, if both taps are on. The same tank can be filled in 60 min, if tap A alone is on. How much time will tap B alone take, to fill up the same tank ?

1. 64 min
2. 80 min
3. 96 min
4. 120 min

Correct Option: D

Part filled by tap A in 1 min = 1/60
Let tap B fills the tank in x min
Then, Part filled by tap, B in 1 min = 1/x
According to the question,
1/60 + 1/x = 1/40
⇒ 1/x = 1/40 - 1/60
&rArr ; 1/x = (3 - 2)/120
&rArr ; 1/x = 1/120
∴ Tap B can fill the tank in 120 min.