Explanation:

- Pipe A can fill the entire tank in 10 minutes, so in 1 minute, it fills 1/10 of the tank.

- Pipe B can fill the entire tank in 25 minutes, so in 1 minute, it fills 1/25 of the tank.

- In the first 5 minutes, both pipes fill together.

- Together, in one minute, they fill \( \frac{1}{10} + \frac{1}{25} = \frac{5}{50} + \frac{2}{50} = \frac{7}{50} \) of the tank.

- In 5 minutes, they fill \( 5 \times \frac{7}{50} = \frac{35}{50} = \frac{7}{10} \) of the tank.

- Now, only \(\frac{3}{10}\) of the tank is left to be filled by Pipe B.

- Pipe B fills \(\frac{1}{25}\) of the tank in one minute.

- To fill \(\frac{3}{10}\) of the tank, it takes \(\frac{3}{10} \div \frac{1}{25} = \frac{3}{10} \times 25 = 7.5\) minutes.

- Option 2: 7.5 minutes is correct.