Queen and Pawn Puzzles

One of our favourite chess puzzles …

Place 8 queens on a chessboard such that none of the queens can take any of the others. Above is a fail – only 5 queens are on the board and they are no places left to put any more.

Here is a website to try yourself to fit 8 queens on the board, it is possible!

We then looked at changing the size of the board from an 8 by 8 to smaller sizes, e.g. can you fit 5 queens on a 5 by 5 board? And if so, how many “unique” solutions are there? We defined a unique solution as being one that did not look like any others we had found when we rotated our paper or put it up to the light so it appeared flipped! Here are our solutions for 5×5, 6×6 and 8×8.

There is a great numberphile video  on this puzzle, and all the answers and stats you could want here.

And finally this great puzzle from Alex Bellos in the Guardian

Can you find a path in which the queen captures all 11 pawns in exactly 11 moves? (The pawns do not move or protect each other.)

Sudoku

Can you create a sudoku?

Think about

  • What would be an efficient way to create a puzzle?
  • How difficult would you like it to be?
  • What is the maximum number of 3×3 squares you could remove and it still be solvable? Does it matter which squares?
  • Could you design it so that it could be easily transformed into mutliple versions? How many versions could be created from your one puzzle?

Here is a fascinating article on how one website generates their sudokus and a paper proving the minimum number of clues needed.

Card game – mod 8!

We played a game posted on youtube by Mr Allen.

Here are his instructions:

This is a card game I made up where you do basic mental calculations and race your opponent ( 2-4 players). Using Ace -10 cards only. Rules: 7 cards are placed face up for each player and two in the middle. The player who gets rid of their cards first wins. You can put a card in the middle (on top of either pile) when one of your cards is an answer to an expression using the two cards in the middle. eg. if 6 and 2 are in the middle possible cards that can be played are 8 (6+2) or 4 (6-2) or 3 (6 divided by 2) or 2 (6×2) – 12 is the answer but we use the last digit only. Each player has to say the expression as they put the card down. eg 6 twos are 12 – placing the 2. or 6 minus/take/sub 2 is 4. all players play on until no cards can be played. Then the dealer deals each player a card then put one on one of the two middle piles. Players then race to place cards until someone gets rid of all their cards! (4 players start with 6 cards)

We played a few games of this and made up our own versions:

  1. Instead of a race we played in turn – competitively or collaboratively
  2. We removed the 9s and 10s and played in mod 8

Cereal Box Problem

Suppose there was one of six toy animals inside your favorite box of cereal and you would like to collect them all.

You could be lucky and only buy six boxes, but how many boxes of cereal would you expect to have to buy on average?

With thanks to this website we carried out an experiment with dice to simulate this problem:

Click here for a pdf with several blank tables to cut out and use.

We then used python to generate 1000 trials and compared our average to the theoretical average we calculated.

Colour Theorem

This activity comes from the great website mathsisfun.com.

Have you ever coloured in a pattern and wondered how many colours you need to use?

There is only one rule

Two sections that share a common edge cannot be colored the same!

Having a common corner is OK, just not an edge.

Let’s start with a simple pattern like a group of nine squares:

nine square grid

What is the minimum colours you need to colour the pattern of nine squares?

A Little More Complicated

How about this one?

circle grid

How many colours do you need this time?

Even More Complicated

Let’s try another:

fancy circle sections

How many colours do you need this time?

Nine? Eight? Seven? Six? Five? Four?

Maps

Things get more interesting if we want to colour a map.

Here is a map of Africa, showing six countries and how they border on each other:

Try colouring in the map and see what is the fewest number of colours you need.

Extension

Can you draw a map with 3 countries such that every country has exactly two neighbours, and then colour it.

Can you draw a map with 4 countries such that every country has exactly two neighbours, and then colour it.

Can you draw a map with 6 countries such that every country has exactly four neighbours, and then colour it.

Can you draw a map with 12 countries such that every country has exactly five neighbours, and then colour it.

Further Reading

The proof of the four colour theorem was famously tricky, and comes from graph theory, where mathematicians investigate an equivalent problem of colouring vertices of a network so that no edge has endpoints the same colour. The original four-colour proof was attempted by Alfred Kempe in 1879, but unfortunately Percy John Heawood found an error 11 years later. However his work was not useless, as Percy was able to prove the five-colour theorem (that one can colour a map with no two adjacent regions the sample colour using at most 5 colours) based on Kempe’s work. The four colour theorem was finally proved in 1976 by Kenneth Appel, Wolfgang Haken, and John Koch using a computer to check it. This was the first major theorem to be proved using a computer. They checked around 1500 configurations using about 1200 hours of computer time. Some people were sceptical about a proof using a computer but independent verification soon convinced everyone that the four colour theorem had finally been proved.

You can read more here.

Conway’s Game of Life

From this great article in Plus magazine

Start with these cells.

The next iteration would be the image below, because all cells survived and three new ones were born.

Can you draw the successive iterations?

You can check your patterns here: https://bitstorm.org/gameoflife/ .

Challenges:

Can you create a starting shape that stays the same?

Can you find a cycle of length 2,3,4 and 5?

You might like to read the article from Plus Maths or even try this question from the 1996 British Informatics Olympiad.