I'm thinking of a number. When my number is divided by 5 the remainder is 4. When my number is divided by 3 the remainder is 2. Can you find my number?

Choose any 3 digits and make a 6 digit number by repeating the 3 digits in the same order (e.g. 594594). Explain why whatever digits you choose the number will always be divisible by 7, 11 and 13.

The number 8888...88M9999...99 is divisible by 7 and it starts with the digit 8 repeated 50 times and ends with the digit 9 repeated 50 times. What is the value of the digit M?

Caroline and James pick sets of five numbers. Charlie chooses three of them that add together to make a multiple of three. Can they stop him?

A three digit number abc is always divisible by 7 when 2a+3b+c is divisible by 7. Why?

A number N is divisible by 10, 90, 98 and 882 but it is NOT divisible by 50 or 270 or 686 or 1764. It is also known that N is a factor of 9261000. What is N?

Find some examples of pairs of numbers such that their sum is a factor of their product. eg. 4 + 12 = 16 and 4 × 12 = 48 and 16 is a factor of 48.

Find the highest power of 11 that will divide into 1000! exactly.

On the planet Vuv there are two sorts of creatures. The Zios have 3 legs and the Zepts have 7 legs. The great planetary explorer Nico counted 52 legs. How many Zios and how many Zepts were there?

How many numbers less than 1000 are NOT divisible by either: a) 2 or 5; or b) 2, 5 or 7?

6! = 6 x 5 x 4 x 3 x 2 x 1. The highest power of 2 that divides exactly into 6! is 4 since (6!) / (2^4 ) = 45. What is the highest power of two that divides exactly into 100!?

I put eggs into a basket in groups of 7 and noticed that I could easily have divided them into piles of 2, 3, 4, 5 or 6 and always have one left over. How many eggs were in the basket?

Find some triples of whole numbers a, b and c such that a^2 + b^2 + c^2 is a multiple of 4. Is it necessarily the case that a, b and c must all be even? If so, can you explain why?

What is the value of the digit A in the sum below: [3(230 + A)]^2 = 49280A

Imagine we have four bags containing a large number of 1s, 4s, 7s and 10s. What numbers can we make?

Is there an efficient way to work out how many factors a large number has?

Number problems at primary level that may require determination.

The five digit number A679B, in base ten, is divisible by 72. What are the values of A and B?

Four of these clues are needed to find the chosen number on this grid and four are true but do nothing to help in finding the number. Can you sort out the clues and find the number?

In this problem we are looking at sets of parallel sticks that cross each other. What is the least number of crossings you can make? And the greatest?

Find the number which has 8 divisors, such that the product of the divisors is 331776.

Using the digits 1, 2, 3, 4, 5, 6, 7 and 8, mulitply a two two digit numbers are multiplied to give a four digit number, so that the expression is correct. How many different solutions can you find?

Look at three 'next door neighbours' amongst the counting numbers. Add them together. What do you notice?

This article takes the reader through divisibility tests and how they work. An article to read with pencil and paper to hand.

48 is called an abundant number because it is less than the sum of its factors (without itself). Can you find some more abundant numbers?

I throw three dice and get 5, 3 and 2. Add the scores on the three dice. What do you get? Now multiply the scores. What do you notice?

Benâ€™s class were cutting up number tracks. First they cut them into twos and added up the numbers on each piece. What patterns could they see?

What happens if you join every second point on this circle? How about every third point? Try with different steps and see if you can predict what will happen.

Three people chose this as a favourite problem. It is the sort of problem that needs thinking time - but once the connection is made it gives access to many similar ideas.

Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some. . . .

What is the lowest number which always leaves a remainder of 1 when divided by each of the numbers from 2 to 10?

Investigate the sum of the numbers on the top and bottom faces of a line of three dice. What do you notice?

Can you find any perfect numbers? Read this article to find out more...

Got It game for an adult and child. How can you play so that you know you will always win?

List any 3 numbers. It is always possible to find a subset of adjacent numbers that add up to a multiple of 3. Can you explain why and prove it?

Can you work out some different ways to balance this equation?

Helen made the conjecture that "every multiple of six has more factors than the two numbers either side of it". Is this conjecture true?

56 406 is the product of two consecutive numbers. What are these two numbers?

Have a go at balancing this equation. Can you find different ways of doing it?

Do you know a quick way to check if a number is a multiple of two? How about three, four or six?

Imagine we have four bags containing numbers from a sequence. What numbers can we make now?

Can you complete this calculation by filling in the missing numbers? In how many different ways can you do it?

What is the remainder when 2^2002 is divided by 7? What happens with different powers of 2?

Can you find a way to identify times tables after they have been shifted up?

Number problems at primary level to work on with others.

For this challenge, you'll need to play Got It! Can you explain the strategy for winning this game with any target?

When the number x 1 x x x is multiplied by 417 this gives the answer 9 x x x 0 5 7. Find the missing digits, each of which is represented by an "x" .

An investigation that gives you the opportunity to make and justify predictions.

Arrange the four number cards on the grid, according to the rules, to make a diagonal, vertical or horizontal line.

Twice a week I go swimming and swim the same number of lengths of the pool each time. As I swim, I count the lengths I've done so far, and make it into a fraction of the whole number of lengths I. . . .