Average speed

10 minutes ago, joigus said:

According to some quantum hype, you could do it with entanglement.  

Nice trick, @TheVat. +1

I must confess I did need a little bit of algebra.

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If you work out the average speed in terms of the two speeds v_1, v_2, you find it's proportional to v_1*v_2/(v_1+v_2) -- the harmonic mean. That's because the overall time is prop. to 1/v_1 + 1/v_2

Some algebra shows that v_2 must be infinite

This is a cute little puzzle.

Yep, I needed algebra as well:

+1