Adding in Rows

List any 3 numbers. It is always possible to find a subset of adjacent numbers that add up to a multiple of 3. Can you explain why and prove it?

Magic Sums and Products

How to build your own magic squares.

Nine, Ten and One

Weekly Problem 3 - 2013
Can you find the value of t in these equations?

No Matter

Stage: 3 Short Challenge Level:

Think of a number, double it, then add $3$. Multiply your answer by $4$ and from this take away $5$. Now also take away the number you first thought of.

No matter what your first number was, your answer will be a multiple of which number?

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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