What’s the fewest number of marks you could put on a 12-inch ruler and still be able to measure every distance from 1 inch to 12 inches?
If you haven’t tried to solve it, have a go now. For everyone else the answer is after the break…
Put marks at 1 inches, 3 inches, 7 inches, and 11 inches. Any other solutions?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.