Father and child make twelve dots on a piece of paper. Now take eleven pennies. Start at any dot, count six dots and let the penny rest on the sixth dot. The object is to place eleven pennies on eleven dots in this manner.
When a penny is resting on a dot you count it the same as a vacant lot, but you must start each count from a vacant dot.
Solution: Start at any dot, count six and place a penny on the sixth dot, but remember where you started. Now start the second penny on a dot so that it comes to rest on the dot where you started the first penny. Start the third penny so that it comes to rest on the dot where you started the second penny, etc. In other words, you work backwards.