There are **37** NRICH Mathematical resources connected to **Combinations**, you may find related items under Decision Mathematics and Combinatorics.

How many pairs of numbers can you find that add up to a multiple of 11? Do you notice anything interesting about your results?

An environment which simulates working with Cuisenaire rods.

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?

How many six digit numbers are there which DO NOT contain a 5?

Liam's house has a staircase with 12 steps. He can go down the steps one at a time or two at time. In how many different ways can Liam go down the 12 steps?

Which of these games would you play to give yourself the best possible chance of winning a prize?

Three children are going to buy some plants for their birthdays. They will plant them within circular paths. How could they do this?

An introduction to the binomial coefficient, and exploration of some of the formulae it satisfies.

This challenging activity involves finding different ways to distribute fifteen items among four sets, when the sets must include three, four, five and six items.

This challenge extends the Plants investigation so now four or more children are involved.

Imagine you had to plan the tour for the Olympic Torch. Is there an efficient way of choosing the shortest possible route?

Can all but one square of an 8 by 8 Chessboard be covered by Trominoes?

A man has 5 coins in his pocket. Given the clues, can you work out what the coins are?

Four friends must cross a bridge. How can they all cross it in just 17 minutes?

Using only the red and white rods, how many different ways are there to make up the other rods?

When you think of spies and secret agents, you probably wouldn’t think of mathematics. Some of the most famous code breakers in history have been mathematicians.

The machine I use to produce Braille messages is faulty and one of the pins that makes a raised dot is not working. I typed a short message in Braille. Can you work out what it really says?

Is it possible to rearrange the numbers 1,2......12 around a clock face in such a way that every two numbers in adjacent positions differ by any of 3, 4 or 5 hours?

Consider all of the five digit numbers which we can form using only the digits 2, 4, 6 and 8. If these numbers are arranged in ascending order, what is the 512th number?

A game that demands a logical approach using systematic working to deduce a winning strategy

Eight children enter the autumn cross-country race at school. How many possible ways could they come in at first, second and third places?

In a league of 5 football teams which play in a round robin tournament show that it is possible for all five teams to be league leaders.

Blue Flibbins are so jealous of their red partners that they will not leave them on their own with any other bue Flibbin. What is the quickest way of getting the five pairs of Flibbins safely to. . . .

In how many distinct ways can six islands be joined by bridges so that each island can be reached from every other island...

In how many ways can you arrange three dice side by side on a surface so that the sum of the numbers on each of the four faces (top, bottom, front and back) is equal?

Is it possible to use all 28 dominoes arranging them in squares of four? What patterns can you see in the solution(s)?

In how many ways can the number 1 000 000 be expressed as the product of three positive integers?

Here is a collection of puzzles about Sam's shop sent in by club members. Perhaps you can make up more puzzles, find formulas or find general methods.

Sam displays cans in 3 triangular stacks. With the same number he could make one large triangular stack or stack them all in a square based pyramid. How many cans are there how were they arranged?

How many tricolour flags are possible with 5 available colours such that two adjacent stripes must NOT be the same colour. What about 256 colours?

Is a score of 9 more likely than a score of 10 when you roll three dice?

How many positive integers less than or equal to 4000 can be written down without using the digits 7, 8 or 9?

To win on a scratch card you have to uncover three numbers that add up to more than fifteen. What is the probability of winning a prize?

Imagine you have six different colours of paint. You paint a cube using a different colour for each of the six faces. How many different cubes can be painted using the same set of six colours?

You and I play a game involving successive throws of a fair coin. Suppose I pick HH and you pick TH. The coin is thrown repeatedly until we see either two heads in a row (I win) or a tail followed by. . . .

There are nine teddies in Teddy Town - three red, three blue and three yellow. There are also nine houses, three of each colour. Can you put them on the map of Teddy Town according to the rules?

Place the 16 different combinations of cup/saucer in this 4 by 4 arrangement so that no row or column contains more than one cup or saucer of the same colour.