A man working alone can do a job in 3 hours. His son can do the same job in 2 hours. How many hours will it take for the two of them together to finish the same job?

The first pipe empties the tank in 30 minutes, so its rate is $\frac{1}{30}$ tank per minute.
The second pipe empties the tank in 20 minutes, so its rate is $\frac{1}{20}$ tank per minute.

When both pipes are open, their rates add up:

To add these fractions, find a common denominator, which is 60:

This means that together, the pipes can empty the entire tank in 12 minutes.

The tank is $\frac{2}{3}$ full, so the amount to be emptied is $\frac{2}{3}$ of the tank's volume.

Time = $\frac{\text{Amount to be emptied}}{\text{Combined rate}}$

The time taken to empty $\frac{2}{3}$ of the tank is 8 minutes.

The final answer is $\text{A) 8 minutes}$.