Addition and subtraction

Ten cards are put into five envelopes so that there are two cards in each envelope. The sum of the numbers inside it is written on each envelope. What numbers could be inside the envelopes?

In this 100 square, look at the green square which contains the numbers 2, 3, 12 and 13. What is the sum of the numbers that are diagonally opposite each other? What do you notice?

Take three consecutive numbers and add them together. What do you notice?

We start with one yellow cube and build around it to make a 3×3×3 cube with red cubes. Then we build around that red cube with blue cubes and so on. How many cubes of each colour have we used?

Can you use the clues to complete these 5 by 5 Mathematical Sudokus?

How many solutions can you find to this sum? Each of the different letters stands for a different number.

A cinema has 100 seats. How can ticket sales make £100 for these different combinations of ticket prices?

Can you arrange these numbers into 7 subsets, each of three numbers, so that when the numbers in each are added together, they make seven consecutive numbers?

Crosses can be drawn on number grids of various sizes. What do you notice when you add opposite ends?

How many ways can you find to put in operation signs (+, −, ×, ÷) to make 100?