There are 28 dominoes in a set, which can be arranged in seven sets of four making a complete link, like the one below.

Is it possible to use all 28 dominoes arranging them in this way? What patterns can you see in the solution(s) and can you explain them? How do you know that you have all the solutions?

You may find our Dominoes Environment useful for working on this problem.

Printable NRICH Roadshow resource.