**From New Scientist #2621, 15th September 2007**

I have nine cards, each of a different colour. On each of the cards is a different non-zero digit. I have spaced the cards evenly round the circumference of a circle. All except the grey card are between an odd digit and an even digit. The hazel, indigo, jade and khaki cards are consecutive in that order clockwise around the circle, with the digits on the first three adding to give the digit on the fourth. The lemon, mauve and navy cards are consecutive in that order clockwise around the circle, with the digits of the first two adding to give double the digit on the third. There is also an orange card.

In some cases the digit on a card equals the sum of its neighbouring two digits. In how many cases? The answer is the digit on the hazel card. Starting at 1, list the numbers and their colours clockwise around the circle (e.g. 1J, 5L …).

[enigma1460]

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Solution:The cards are 1G, 3H, 2I, 4J, 9K, 5O, 8L, 6M, 7N.