Tap A can fill a tank in 8 minutes while tap B empties it in 9 minutes. How long will the tank be full if the two taps are opened at the same time?

Answer 1

1/8 - 1/9 = 1/72

That's how much of the tank gets filled in one minute with both taps open, right?

But the question is poorly worded...

Answer 2

1/24