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There are exactly 3 ways to add 4 odd numbers to get 10. Find all the ways of adding 8 odd numbers to get 20. To be sure of getting all the solutions you will need to be systematic. What about a total of 15 with 6 odd numbers?

Always the Same

Stage: 3 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

Arrange the numbers 1 to 16 into a 4 by 4 array.

Choose a number and circle it. Cross out the numbers which are in the same row and column as your chosen number.

Repeat this process twice more choosing from the remaining numbers.

This should leave you with one number remaining, circle this one also.

Add up your four circled numbers.

Why do they always add up to 34 whatever way you choose your numbers?