i. A is kept open first, followed by B and then C
Each cycle of 3 minutes, 75 liters get filled. 100 + 25 - 50. So, after 3 minutes the tank would have 75 liters
6 mins - 150 liters
9 mins - 225 liters
30 mins - 750 liters
270 mins - 6750 liters
273 mins - 6825 liters
276 mins - 6900 litres
During the 277th min, Pipe A is Opened and it fills at the rate of 100 litres/min. Therefore, at the end of 277 mins, the tank is filled.
The most important thing in these type of questions is to think in terms of cycles till we reach close to the required target and then think in simple steps.
ii. B first, followed by A, and then C
Each cycle of 3 minutes, 75 liters get filled. 25 + 100 - 50. So, after 3 minutes the tank would have 75 liters.
6 mins - 150 liters
9 mins - 225 liters
30 mins - 750 liters
270 mins - 6750 liters
273 mins - 6825 liters
276 mins - 6900 litres
During the 277th min, Pipe B is Opened and it fills at the rate of 25 litres/min. At the end of 277 mins, 6925 litres.
Then, Pipe A is opened and it fills at the rate of 100 litres/min. Therefore, it takes 3/4 th of a minute to fill the remaining 75 litres.
Time taken = 277 + 3/4 th minute = 277 mins and 45 secs .
iii. B first, followed by C, and then A
In this case also, Each cycle of 3 minutes, 75 litres get filled. 25 -50 + 100. But there is a small catch here. In the first set of 3 minutes, we would fill up to about 100 litres. After 1 minute, we would be at 25 liters, after 2 minutes, we would be at 0 liters and in the third minute, the tank would be 100 litres full.
6 mins - 175 liters
9 mins - 250 liters
30 mins - 775 liters
270 mins - 6775 liters
273 mins - 6850 liters
276 mins - 6925 liters
279 minutes - 7000 liters
So, it would take 279 mins to fill the tank.
The most important thing in these type of questions is to think in terms of cycles till we reach close to the required target and then think in simple steps.
Answer Choice (D).
Correct Answer: 277 mins, 277 mins and 45 secs and 279 mins