Description for Correct answer:
Tap A can fill the tank in 30 minutes. Therefore, it fills \( \Large \frac{1}{30} \)th of the tank every minute.

Tap B can fill the tank in 60 minutes. Therefore, it fills \( \Large \frac{1}{60} \)th of the tank every minute.

Together, the two taps will fill \( \Large \frac{1}{30}+\frac{1}{60}=\frac{2+1}{60}=\frac{3}{60}=\frac{1}{20} \)th of the tank every minute.

Therefore, when both the taps are opened simultaneously, they will fill the tank in 20 minutes. As the tank is already half full, they need to fill only half the tank.

Therefore, the tank will overflow 10 minutes after both the taps are opened.