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These two group activities use mathematical reasoning - one is numerical, one geometric.

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Round and Round the Circle

What happens if you join every second point on this circle? How about every third point? Try with different steps and see if you can predict what will happen.

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Strange Numbers

All strange numbers are prime. Every one digit prime number is strange and a number of two or more digits is strange if and only if so are the two numbers obtained from it by omitting either its first or its last digit. Find all strange numbers.

Weekly Problem 6 - 2010

Stage: 2 and 3 Short Challenge Level: Challenge Level:1

How many sets of three prime numbers have the property that the product of the three numbers is exactly five times their sum? (The order of the three numbers is not important).

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

 

 

This problem is taken from the UKMT Mathematical Challenges.

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