![Placeholder: several colourful numbers](/themes/nrich/images/nrich_small_placeholder.png)
Permutations
![Placeholder: several colourful numbers](/themes/nrich/images/nrich_small_placeholder.png)
![Colourful Tiles](/sites/default/files/styles/medium/public/thumbnails/content-id-7169-icon.png?itok=J5nVpoAA)
problem
Colourful Tiles
Weekly Problem 21 - 2011
How many ways can you paint this wall with four different colours?
How many ways can you paint this wall with four different colours?
![Oranges and Lemons, say the bells of St Clement's](/sites/default/files/styles/medium/public/thumbnails/content-id-5341-icon.jpg?itok=gfre-Q6W)
problem
Oranges and Lemons, say the bells of St Clement's
Bellringers have a special way to write down the patterns they
ring. Learn about these patterns and draw some of your own.
![Bell Ringing](/sites/default/files/styles/medium/public/thumbnails/content-97-10-six11-icon.jpg?itok=Qm_3uE-r)
problem
Bell Ringing
Suppose you are a bellringer. Can you find the changes so that,
starting and ending with a round, all the 24 possible permutations
are rung once each and only once?
![Even Up](/sites/default/files/styles/medium/public/thumbnails/content-97-10-six7-icon.jpg?itok=-SHLzknC)
problem
Even Up
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?
![Voting Paradox](/sites/default/files/styles/medium/public/thumbnails/content-98-08-15plus3-icon.jpg?itok=dOfDsWF_)
problem
Voting Paradox
Some relationships are transitive, such as `if A>B and B>C
then it follows that A>C', but some are not. In a voting system,
if A beats B and B beats C should we expect A to beat C?
![Six times five](/sites/default/files/styles/medium/public/thumbnails/content-03-09-six4-icon.gif?itok=lQUAWZbA)
![396](/sites/default/files/styles/medium/public/thumbnails/content-96-11-six5-icon.jpg?itok=tKPhuRLl)
problem
396
The four digits 5, 6, 7 and 8 are put at random in the spaces of
the number : 3 _ 1 _ 4 _ 0 _ 9 2 Calculate the probability that the
answer will be a multiple of 396.
![Chances are](/sites/default/files/styles/medium/public/thumbnails/content-03-06-six3-icon.gif?itok=2eqi9Gd4)
problem
Chances are
Which of these games would you play to give yourself the best possible chance of winning a prize?
![Master Minding](/sites/default/files/styles/medium/public/thumbnails/content-03-05-six1-icon.gif?itok=6GWL_6VQ)
problem
Master Minding
Your partner chooses two beads and places them side by side behind a screen. What is the minimum number of guesses you would need to be sure of guessing the two beads and their positions?