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Prime Magic

Stage: 2, 3 and 4 Challenge Level: Challenge Level:2 Challenge Level:2

Place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3 grid so that all the rows and columns add up to a prime number. Two solutions are considered to be the same if, as in the example shown, they contain the same six triples. How many different solutions can you find?

2 8 3
6 4 9
5 7 1

2 3 8
5 1 7
6 9 4

Show that it is impossible to place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3 grid so that the diagonals, as well as all the rows and columns, add up to prime numbers.

Printable NRICH Roadshow resource.