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115^2 = (110 x 120) + 25, that is 13225 895^2 = (890 x 900) + 25, that is 801025 Can you explain what is happening and generalise?
Three people chose this as a favourite problem. It is the sort of problem that needs thinking time - but once the connection is made it gives access to many similar ideas.
This article takes the reader through divisibility tests and how they work. An article to read with pencil and paper to hand.
Each letter represents a different positive digit AHHAAH / JOKE = HA What are the values of each of the letters?
Given any 3 digit number you can use the given digits and name another number which is divisible by 37 (e.g. given 628 you say 628371 is divisible by 37 because you know that 6+3 = 2+7 = 8+1 = 9). . . .
Explore the factors of the numbers which are written as 10101 in different number bases. Prove that the numbers 10201, 11011 and 10101 are composite in any base.
Make a line of green and a line of yellow rods so that the lines differ in length by one (a white rod)
In how many ways can the number 1 000 000 be expressed as the product of three positive integers?
What is the largest number which, when divided into 1905, 2587, 3951, 7020 and 8725 in turn, leaves the same remainder each time?
Data is sent in chunks of two different sizes - a yellow chunk has 5 characters and a blue chunk has 9 characters. A data slot of size 31 cannot be exactly filled with a combination of yellow and. . . .
Consider numbers of the form un = 1! + 2! + 3! +...+n!. How many such numbers are perfect squares?
Take any two digit number, for example 58. What do you have to do to reverse the order of the digits? Can you find a rule for reversing the order of digits for any two digit number?
Here is a Sudoku with a difference! Use information about lowest common multiples to help you solve it.
Imagine we have four bags containing numbers from a sequence. What numbers can we make now?
The puzzle can be solved by finding the values of the unknown digits (all indicated by asterisks) in the squares of the $9\times9$ grid.
A collection of resources to support work on Factors and Multiples at Secondary level.
The number 12 = 2^2 × 3 has 6 factors. What is the smallest natural number with exactly 36 factors?
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?
Substitution and Transposition all in one! How fiendish can these codes get?
How many numbers less than 1000 are NOT divisible by either: a) 2 or 5; or b) 2, 5 or 7?
Can you work out what size grid you need to read our secret message?
You are given the Lowest Common Multiples of sets of digits. Find the digits and then solve the Sudoku.
Helen made the conjecture that "every multiple of six has more factors than the two numbers either side of it". Is this conjecture true?
Find the number which has 8 divisors, such that the product of the divisors is 331776.
How many zeros are there at the end of the number which is the product of first hundred positive integers?
I'm thinking of a number. When my number is divided by 5 the remainder is 4. When my number is divided by 3 the remainder is 2. Can you find my number?
What is the value of the digit A in the sum below: [3(230 + A)]^2 = 49280A
Prove that if a^2+b^2 is a multiple of 3 then both a and b are multiples of 3.
A number N is divisible by 10, 90, 98 and 882 but it is NOT divisible by 50 or 270 or 686 or 1764. It is also known that N is a factor of 9261000. What is N?
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?
The five digit number A679B, in base ten, is divisible by 72. What are the values of A and B?
The sum of the first 'n' natural numbers is a 3 digit number in which all the digits are the same. How many numbers have been summed?
A three digit number abc is always divisible by 7 when 2a+3b+c is divisible by 7. Why?
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?
The clues for this Sudoku are the product of the numbers in adjacent squares.
Can you find a way to identify times tables after they have been shifted up?
A game that tests your understanding of remainders.
In this activity, the computer chooses a times table and shifts it. Can you work out the table and the shift each time?
Here is a machine with four coloured lights. Can you develop a strategy to work out the rules controlling each light?
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. . . .
Imagine we have four bags containing a large number of 1s, 4s, 7s and 10s. What numbers can we make?
Have you seen this way of doing multiplication ?
Follow this recipe for sieving numbers and see what interesting patterns emerge.
Can you find any perfect numbers? Read this article to find out more...
What is the smallest number of answers you need to reveal in order to work out the missing headers?
Find the highest power of 11 that will divide into 1000! exactly.
Which pairs of cogs let the coloured tooth touch every tooth on the other cog? Which pairs do not let this happen? Why?
How many integers between 1 and 1200 are NOT multiples of any of the numbers 2, 3 or 5?
Given the products of diagonally opposite cells - can you complete this Sudoku?
Complete the following expressions so that each one gives a four digit number as the product of two two digit numbers and uses the digits 1 to 8 once and only once.