NDB Range RNAV

There are two formulas for the range of an NDBNDB —Non-Directional Beacon:

• $3\sqrt{P}$ for transmission over the sea
• $2\sqrt{P}$ for transmission over the land

where $P$ is the power of the transmission. The difference comes from lesser attenuation over the sea.

As ever with mathematical questions, ensure the examiner has not tricked you by putting the answers in an unusual unit – this particular formula outputs in nautical miles, so watch for the "correct" number with km attached to it.