Main content

Today Puzzle #602

Puzzle No. 602– Friday 1 November

A 5p coin whose diameter is about 25mm is tossed onto a chess board with 50mm squares. In one hundred tosses how many of these would you expect the coin to end up on exactly two squares?

Today’s #PuzzleForToday has been set by Hugh Hunt, Reader in Engineering Dynamics and Vibration at Trinity College, Cambridge

Click here for the answer


Up-down and left-right are independent coordinates for the position of the coin on the board. The probability of covering two squares is 0.5 in each of these directions so it's just like the probability with two coins getting HH, HT, TH or TT. HT and TH are the equivalent of landing on two squares only so the answer is 50%.

More fiendish brain-teasers and quizzes on BBC Radio...