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# Average speed and percentage

By Murray Bourne, 07 May 2009

This kind of puzzle always catch out students.

I travel to work at 30 km/h, but on the way home there is less traffic so I can travel at 60 km/h. What is my average speed?

And the second one is also an old favourite.

I have a jar of water and I remove 10% of it. Then my friend comes along and increases the amount of water by 10%. Is there more, the same or less water in the jar than when we started?

I'll offer a prize to the first correct answers with good reasoning. What prize?

You will get a warm inner glow for having achieved something. 🙂

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