Explanation:

- The tank fills at different rates with each tap:

- Tap A fills the tank in 10 hours (1/10 of the tank per hour).

- Tap B fills the tank in 20 hours (1/20 of the tank per hour).

- Tap C fills the tank in 25 hours (1/25 of the tank per hour).

- When all three taps are open:

- Combined rate = 1/10 + 1/20 + 1/25 = (10 + 5 + 4)/100 = 19/100 per hour.

- In the first 2 hours, they fill 2 * 19/100 = 38/100 of the tank.

- Tap C is then closed:

- Combined rate of A and B = 1/10 + 1/20 = 3/20 per hour.

- In the next 4 hours, they fill 4 * 3/20 = 12/20 = 60/100 of the tank.

- Together in 6 hours, 38/100 + 60/100 = 98/100 of the tank is filled.

- Remaining 1/50 of the tank is filled by tap A alone:

- Tap A fills 1/10 per hour, so it takes 1/5 hours more.

- Total work by tap A:

- In 6 hours, tap A fills 1/10 * 6 = 6/10.

- Plus the extra 1/50, tap A fills 6/10 + 1/50 = 31/50 of the tank.

- Calculate percentage contributed by tap A:

- (31/50) * 100 = 62%.

- Option 2 - 52% is correct.