Explanation:

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

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

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

Let’s break it down:

- First 2 hours: All three are open, so work = 2 × (1/10 + 1/20 + 1/25)

= 2 × (0.1 + 0.05 + 0.04) = 2 × 0.19 = 0.38

- Next 2 hours: A and B are open, so work = 2 × (1/10 + 1/20) = 2 × 0.15 = 0.3

- Next 2 hours: Only A is open, so work = 2 × (1/10) = 0.2

- Total after 6 hours: 0.38 + 0.3 + 0.2 = 0.88 (88% filled)

Remaining: 1 - 0.88 = 0.12 (12% left)

- Tap A fills the remaining 12% alone. Time needed = 0.12 × 10 = 1.2 hours

- Total work by A:

- First 2 hours: 2 × (1/10) = 0.2

- Next 2 hours: 2 × (1/10) = 0.2

- Next 2 hours: 2 × (1/10) = 0.2

- Finally, 1.2 × (1/10) = 0.12

- Total = 0.2 + 0.2 + 0.2 + 0.12 = 0.72 (72%)

Option analysis:

- Option 1: 75% – Incorrect

- Option 2: 52% – Incorrect

- Option 3: 72% – Correct

- Option 4: 32% – Incorrect