Addition and subtraction

This addition sum uses all ten digits 0, 1, 2...9 exactly once. Find the sum and show that the one you give is the only possibility.

If you wrote all the possible four digit numbers made by using each of the digits 2, 4, 5, 7 once, what would they add up to?

The country Sixtania prints postage stamps with only three values 6 lucres, 10 lucres and 15 lucres (where the currency is in lucres).Which values cannot be made up with combinations of these postage stamps? Prove that all other values can be made up.

What is happening at each box in these machines?

If the odd numbers on two dice are made negative, which of the totals cannot be achieved?

What is the value of c in this subtraction?

In this investigation, you are challenged to make mobile phone numbers which are easy to remember. What happens if you make a sequence adding 2 each time?

Can you solve this magic square?

Tony and Tina can't work out which of them owes what to the other. Can you?

Arrange these three famous mathematicians in order with the shortest-lived first.