You may also like

Calendar Capers

Choose any three by three square of dates on a calendar page...

Adding All Nine

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 other possibilities for yourself!

Always the Same

Arrange the numbers 1 to 16 into a 4 by 4 array. Choose a number. Cross out the numbers on the same row and column. Repeat this process. Add up you four numbers. Why do they always add up to 34?

Winning Team

Age 11 to 14
Challenge Level

Helen, Lucy, Rosy, Becki, Jo and Morven, from The Mount School, York and Henry of St Peter's School, Adelaide all found that the three teams scored an equal number of points so that deciding on the winning team presents difficulties. James of Hethersett High School, Norwich gave the race results as follows.

(1) X v Y

Teams  X Y Y X X Y
Runners    A B D F H I
Points  6 5 4 3 2 1

Team X 11 points, team Y 10 points so X beats Y.

(2) Y v Z

Teams  Y Z Y Z Z Y
Runners    B C D E G I
Points  6 5 4 3 2 1

Team Y 11 points, team Z 10 points so Y beats Z.

(3) X v Z

Teams  X Z Z X Z X
Runners    A C E F G H
Points  6 5 4 3 2 1

Team X 10 points, team Z 11 points so Z beats X.

Adding the points for the races together each team scores 21 points.

These results are very peculiar because each team scored an equal number of points. This means that the judge has to look at which team came first in the three races. As team X beat Y in the first race and team Y beat Z in the second you would expect that, with the same runners finishing in the same order, X must surely beat Z in the third race. This does not happen so you cannot decide on a winning team. You might say X are the winning team because they have the champion runner in their team, but then Z could complain because they beat X.

Compare this idea to the relation of `greater than' for numbers. For example if x, y and z are numbers and we know that x > y and y > z then it must follow that x > z. It follows because x is to the right of y on the number line and y is to the right of z. This relation is called `transitivity' in mathematics and we come to expect it, so when a relation arises that is not transitive, as in this example, it comes as a surprise. What seems obvious is not always true, so when you think you have a mathematical result you might be wrong. You must always prove a result before you can be sure it is true.