Mental calculations

The sum of the numbers inside an envelope is written on the outside. What could the numbers be?

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

Investigate how you can work out what day of the week your birthday will be on next year, and the year after...

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?

Mathematicians are always looking for efficient methods for solving problems. How efficient can you be?

Can you work out which drink has the stronger flavour?

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

Charlie and Abi put a counter on 42. They wondered if they could visit all the other numbers on their 1-100 board, moving the counter using just these two operations: ×2 and -5. What do you think?

Here's a chance to work with large numbers...

Can you find ways to put numbers in the overlaps so the rings have equal totals?