Find some examples of pairs of numbers such that their sum is a factor of their product. eg. 4 + 12 = 16 and 4 × 12 = 48 and 16 is a factor of 48.
Ben passed a third of his counters to Jack, Jack passed a quarter of his counters to Emma and Emma passed a fifth of her counters to Ben. After this they all had the same number of counters.
Do you know a quick way to check if a number is a multiple of two? How about three, four or six?
A game for two people, or play online. Given a target number, say 23, and a range of numbers to choose from, say 1-4, players take it in turns to add to the running total to hit their target.
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?
Is there an efficient way to work out how many factors a large number has?
A three digit number abc is always divisible by 7 when 2a+3b+c is divisible by 7. Why?
Imagine we have four bags containing a large number of 1s, 4s, 7s and 10s. What numbers can we make?
List any 3 numbers. It is always possible to find a subset of adjacent numbers that add up to a multiple of 3. Can you explain why and prove it?
Imagine we have four bags containing numbers from a sequence. What numbers can we make now?
Can you explain the strategy for winning this game with any target?
Choose any 3 digits and make a 6 digit number by repeating the 3 digits in the same order (e.g. 594594). Explain why whatever digits you choose the number will always be divisible by 7, 11 and 13.
Play the divisibility game to create numbers in which the first two digits make a number divisible by 2, the first three digits make a number divisible by 3...
The clues for this Sudoku are the product of the numbers in adjacent squares.
Rectangles are considered different if they vary in size or have different locations. How many different rectangles can be drawn on a chessboard?
Can you find any two-digit numbers that satisfy all of these statements?
Katie and Will have some balloons. Will's balloon burst at exactly the same size as Katie's at the beginning of a puff. How many puffs had Will done before his balloon burst?
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. . . .
Using the digits 1 to 9, the number 4396 can be written as the product of two numbers. Can you find the factors?
A mathematician goes into a supermarket and buys four items. Using a calculator she multiplies the cost instead of adding them. How can her answer be the same as the total at the till?
Find a cuboid (with edges of integer values) that has a surface area of exactly 100 square units. Is there more than one? Can you find them all?
Twice a week I go swimming and swim the same number of lengths of the pool each time. As I swim, I count the lengths I've done so far, and make it into a fraction of the whole number of lengths I. . . .
Can you find a way to identify times tables after they have been shifted up?
I throw three dice and get 5, 3 and 2. Add the scores on the three dice. What do you get? Now multiply the scores. What do you notice?
Given the products of adjacent cells, can you complete this Sudoku?
A game that tests your understanding of remainders.
Are these statements always true, sometimes true or never true?
The five digit number A679B, in base ten, is divisible by 72. What are the values of A and B?
What is the smallest number of answers you need to reveal in order to work out the missing headers?
Investigate the sum of the numbers on the top and bottom faces of a line of three dice. What do you notice?
The discs for this game are kept in a flat square box with a square hole for each disc. Use the information to find out how many discs of each colour there are in the box.
An investigation that gives you the opportunity to make and justify predictions.
What is the lowest number which always leaves a remainder of 1 when divided by each of the numbers from 2 to 10?
Gabriel multiplied together some numbers and then erased them. Can you figure out where each number was?
Can you find a relationship between the number of dots on the circle and the number of steps that will ensure that all points are hit?
Got It game for an adult and child. How can you play so that you know you will always win?
In this problem we are looking at sets of parallel sticks that cross each other. What is the least number of crossings you can make? And the greatest?
These red, yellow and blue spinners were each spun 45 times in total. Can you work out which numbers are on each spinner?
What happens if you join every second point on this circle? How about every third point? Try with different steps and see if you can predict what will happen.
Look at three 'next door neighbours' amongst the counting numbers. Add them together. What do you notice?
This article for teachers describes how number arrays can be a useful reprentation for many number concepts.
The number 8888...88M9999...99 is divisible by 7 and it starts with the digit 8 repeated 50 times and ends with the digit 9 repeated 50 times. What is the value of the digit M?
Ben’s class were cutting up number tracks. First they cut them into twos and added up the numbers on each piece. What patterns could they see?
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?
How can you use just one weighing to find out which box contains the lighter ten coins out of the ten boxes?
Number problems at primary level that may require resilience.
Arrange the four number cards on the grid, according to the rules, to make a diagonal, vertical or horizontal line.
What is the value of the digit A in the sum below: [3(230 + A)]^2 = 49280A
What is the remainder when 2^2002 is divided by 7? What happens with different powers of 2?
I put eggs into a basket in groups of 7 and noticed that I could easily have divided them into piles of 2, 3, 4, 5 or 6 and always have one left over. How many eggs were in the basket?