Weekly Brainteaser 29/02/2016

A helicopter covers its outward journey at 252 mph.

It returns, over exactly the same distance, at 189 mph.

What is the helicopter’s average speed over the entire journey?

Answers on paper, with full name and form to Mrs Wardle by Monday 7th March, break time. Please feel free to place your answer under my door, or email if you are unable to find me.