Are these statements always true, sometimes true or never true?
Look at what happens when you take a number, square it and subtract your answer. What kind of number do you get? Can you prove it?
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?
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. . . .
Look at three 'next door neighbours' amongst the counting numbers. Add them together. What do you notice?
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?
Are these statements relating to odd and even numbers always true, sometimes true or never true?
Can you find different ways of creating paths using these paving slabs?
Powers of numbers behave in surprising ways. Take a look at some of these and try to explain why they are true.
Use your logical reasoning to work out how many cows and how many sheep there are in each field.
What happens when you add three numbers together? Will your answer be odd or even? How do you know?
Imagine we have four bags containing numbers from a sequence. What numbers can we make now?
Three dice are placed in a row. Find a way to turn each one so that the three numbers on top of the dice total the same as the three numbers on the front of the dice. Can you find all the ways to do. . . .
Consider the equation 1/a + 1/b + 1/c = 1 where a, b and c are natural numbers and 0 < a < b < c. Prove that there is only one set of values which satisfy this equation.
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?
Replace each letter with a digit to make this addition correct.
Use the numbers in the box below to make the base of a top-heavy pyramid whose top number is 200.
How many pairs of numbers can you find that add up to a multiple of 11? Do you notice anything interesting about your results?
Choose any three by three square of dates on a calendar page...
Who said that adding couldn't be fun?
What are the missing numbers in the pyramids?
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?
This article introduces the idea of generic proof for younger children and illustrates how one example can offer a proof of a general result through unpacking its underlying structure.
You have been given nine weights, one of which is slightly heavier than the rest. Can you work out which weight is heavier in just two weighings of the balance?
Imagine we have four bags containing a large number of 1s, 4s, 7s and 10s. What numbers can we make?
This addition sum uses all ten digits 0, 1, 2...9 exactly once. Find the sum and show that the one you give is the only possibility.
In the following sum the letters A, B, C, D, E and F stand for six distinct digits. Find all the ways of replacing the letters with digits so that the arithmetic is correct.
You can work out the number someone else is thinking of as follows. Ask a friend to think of any natural number less than 100. Then ask them to tell you the remainders when this number is divided by. . . .
Can you arrange the numbers 1 to 17 in a row so that each adjacent pair adds up to a square number?
Which hexagons tessellate?
A huge wheel is rolling past your window. What do you see?
Are these statements always true, sometimes true or never true?
Can you cross each of the seven bridges that join the north and south of the river to the two islands, once and once only, without retracing your steps?
When number pyramids have a sequence on the bottom layer, some interesting patterns emerge...
A game for 2 players that can be played online. Players take it in turns to select a word from the 9 words given. The aim is to select all the occurrences of the same letter.
Carry out cyclic permutations of nine digit numbers containing the digits from 1 to 9 (until you get back to the first number). Prove that whatever number you choose, they will add to the same total.
There are four children in a family, two girls, Kate and Sally, and two boys, Tom and Ben. How old are the children?
If you can copy a network without lifting your pen off the paper and without drawing any line twice, then it is traversable. Decide which of these diagrams are traversable.
In how many distinct ways can six islands be joined by bridges so that each island can be reached from every other island...
If you know the sizes of the angles marked with coloured dots in this diagram which angles can you find by calculation?
From a group of any 4 students in a class of 30, each has exchanged Christmas cards with the other three. Show that some students have exchanged cards with all the other students in the class. How. . . .
This jar used to hold perfumed oil. It contained enough oil to fill granid silver bottles. Each bottle held enough to fill ozvik golden goblets and each goblet held enough to fill vaswik crystal. . . .
Baker, Cooper, Jones and Smith are four people whose occupations are teacher, welder, mechanic and programmer, but not necessarily in that order. What is each person’s occupation?
A standard die has the numbers 1, 2 and 3 are opposite 6, 5 and 4 respectively so that opposite faces add to 7? If you make standard dice by writing 1, 2, 3, 4, 5, 6 on blank cubes you will find. . . .
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. . . .
Write down a three-digit number Change the order of the digits to get a different number Find the difference between the two three digit numbers Follow the rest of the instructions then try. . . .
Six points are arranged in space so that no three are collinear. How many line segments can be formed by joining the points in pairs?
Do you know how to find the area of a triangle? You can count the squares. What happens if we turn the triangle on end? Press the button and see. Try counting the number of units in the triangle now. . . .
ABC is an equilateral triangle and P is a point in the interior of the triangle. We know that AP = 3cm and BP = 4cm. Prove that CP must be less than 10 cm.
Eight children enter the autumn cross-country race at school. How many possible ways could they come in at first, second and third places?