You have 15 cards numbered one to 15 and you must place these 15 cards in a triangle; five cards on the bottom row, four on the next, and so on until you place one card in the top row.
You will notice that each card, except those in the bottom row, is above two cards in the row below.
The challenge is to place the 15 cards such that the value on each card, except those in the bottom row, is the difference between the two cards below it.
Can you solve the puzzle?
The top card is 5,
Supported by 4 and 9,
The middle row is 7, 11 and 2,
Beneath those are 8, 1, 12 and 10,
With a bottom row of 6, 14, 15, 3 and 13.