Explaining, convincing and proving

What is the smallest number of jelly babies Tom must take, to be certain that he gets at least one of each flavour?

Weekly Problem 32 - 2015
Can you work out the missing numbers in this multiplication magic square?

Can you work out the values of J, M and C in this sum?

Weekly Problem 8 - 2016
Can you work out the size of the angles in a quadrilateral?

Weekly Problem 39 - 2016
In the diagram, VWX and XYZ are congruent equilateral triangles. What is the size of angle VWY?

Peter wrote a list of all the numbers that can be formed by changing one digit of the number 200. How many of Peter's numbers are prime?

Four cards have a number on one side and a phrase on the back. On each card, the number does not have the property described on the back. What do the four cards have on them?

Weekly Problem 38 - 2017
In the diagram, what is the value of $x$?

You may have met Magic Squares, now meet an Anti-Magic Square. Its properties are slightly different - can you still solve it?

Prove that sqrt2, sqrt3 and sqrt5 cannot be terms of ANY arithmetic progression.