**New Scientist #2683, 22nd November 2008** [link]

Pleasure boats ply in each direction along the canal from Eastbridge to Westford and back. They leave each place on the hour and every 15 minutes.

One day I left Eastbridge to walk along the towpath to Westford. I left at 12 o’clock and arrived at Westford at the same time as the boat that had left Eastbridge at 12.15. On my walk I saw eight boats going in the opposite direction, including one which arrived at Eastbridge as I left, and one which left Westford as I arrived.

The next day I left Eastbridge to cycle along the towpath to Westford at 6 kilometres per hour faster than I walked. Again, I left at 12 o’clock but this time I arrived at Westford at the same time as the boat which had left Eastbridge at 11.45. On my walk I saw six boats going in the opposite direction, including one which arrived at Eastbridge as I left, and one which left Westford as I arrived.

What is the speed of the boats?

[enigma1521]

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I didn’t program this one, as the result was apparent with a little analysis…

Solution:The boats travel at 8 km/h.