Three taps A, B, C can fill an overhead tank in 4, 6 and 12 hours respectively. How long would the three taps take to fill the tank if all of them are opened together ?

Time taken by tap A to fill the tank in one hour = $$\frac{1}{4}$$ 

Time taken by tap B to fill the tank in one hour = $$\frac{1}{6}$$ 

Time taken by tap C to fill the tank in one hour = $$\frac{1}{12}$$ 

Time taken by all taps to fill the tank in one hour = $$\frac{1}{4} + \frac{1}{6} + \frac{1}{12}$$ or $$\frac{6}{12}$$ or $$\frac{1}{2}$$

Total time taken by all three taps together to fill the tank = 2 hours.

Hence, option A is the correct answer.