Prime numbers

problem
Xavi's T-shirt

Age

7 to 16

Challenge level

How much can you read into a T-shirt?
game
Favourite

Dicey array

Age

5 to 11

Challenge level

Watch the video of this game being played. Can you work out the rules? Which dice totals are good to get, and why?
article
Public key cryptography

An introduction to coding and decoding messages and the maths behind how to secretly share information.
game

Factors and multiples game for two

Age

7 to 14

Challenge level

Factors and Multiples game for an adult and child. How can you make sure you win this game?
problem
Prime counter

Age

16 to 18

Challenge level

A short challenge concerning prime numbers.
problem
Sieve of Eratosthenes

Age

11 to 14

Challenge level

Follow this recipe for sieving numbers and see what interesting patterns emerge.
problem
Number families

Age

11 to 14

Challenge level

How many different number families can you find?
problem
HCF expression

Age

11 to 14

Challenge level

Find out which two distinct primes less than $7$ will give the largest highest common factor of these two expressions.
problem
Three primes

Age

14 to 16

Challenge level

Weekly Problem 6 - 2010
Can you find three primes such that their product is exactly five times their sum? Do you think you have found all possibilities?
problem
How much can we spend?

Age

11 to 14

Challenge level

A country has decided to have just two different coins, 3z and 5z coins. Which totals can be made? Is there a largest total that cannot be made? How do you know?