Can you work out what size grid you need to read our secret message?
Substitution and Transposition all in one! How fiendish can these codes get?
This article takes the reader through divisibility tests and how they work. An article to read with pencil and paper to hand.
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. . . .
Here is a Sudoku with a difference! Use information about lowest common multiples to help you solve it.
Make a line of green and a line of yellow rods so that the lines
differ in length by one (a white rod)
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.
In how many ways can the number 1 000 000 be expressed as the
product of three positive integers?
You are given the Lowest Common Multiples of sets of digits. Find
the digits and then solve the Sudoku.
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.
How many zeros are there at the end of the number which is the
product of first hundred positive integers?
The clues for this Sudoku are the product of the numbers in adjacent squares.
Each letter represents a different positive digit
AHHAAH / JOKE = HA
What are the values of each of the letters?
What is the largest number which, when divided into 1905, 2587,
3951, 7020 and 8725 in turn, leaves the same remainder each time?
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). . . .
Consider numbers of the form un = 1! + 2! + 3! +...+n!. How many such numbers are perfect squares?
When the number x 1 x x x is multiplied by 417 this gives the
answer 9 x x x 0 5 7. Find the missing digits, each of which is
represented by an "x" .
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.
How many numbers less than 1000 are NOT divisible by either: a) 2
or 5; or b) 2, 5 or 7?
What is the remainder when 2^2002 is divided by 7? What happens
with different powers of 2?
The five digit number A679B, in base ten, is divisible by 72. What
are the values of A and B?
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?
A collection of resources to support work on Factors and Multiples at Secondary level.
A game that tests your understanding of remainders.
Find the highest power of 11 that will divide into 1000! exactly.
Given the products of diagonally opposite cells - can you complete this Sudoku?
6! = 6 x 5 x 4 x 3 x 2 x 1. The highest power of 2 that divides
exactly into 6! is 4 since (6!) / (2^4 ) = 45. What is the highest
power of two that divides exactly into 100!?
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?
What is the value of the digit A in the sum below: [3(230 + A)]^2 =
Find the frequency distribution for ordinary English, and use it to help you crack the code.
Explain why the arithmetic sequence 1, 14, 27, 40, ... contains many terms of the form 222...2 where only the digit 2 appears.
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?
Find the number which has 8 divisors, such that the product of the
divisors is 331776.
The number 12 = 2^2 × 3 has 6 factors. What is the smallest natural number with exactly 36 factors?
Can you find a way to identify times tables after they have been shifted up?
Prove that if a^2+b^2 is a multiple of 3 then both a and b are multiples of 3.
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?
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?
Can you find any perfect numbers? Read this article to find out more...
For this challenge, you'll need to play Got It! Can you explain the strategy for winning this game with any 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?
Using the digits 1, 2, 3, 4, 5, 6, 7 and 8, mulitply a two two
digit numbers are multiplied to give a four digit number, so that
the expression is correct. How many different solutions can you
How many integers between 1 and 1200 are NOT multiples of any of
the numbers 2, 3 or 5?
Caroline and James pick sets of five numbers. Charlie chooses three of them that add together to make a multiple of three. Can they stop him?
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.
Helen made the conjecture that "every multiple of six has more
factors than the two numbers either side of it". Is this conjecture
Follow this recipe for sieving numbers and see what interesting patterns emerge.
Factorial one hundred (written 100!) has 24 noughts when written in full and that 1000! has 249 noughts? Convince yourself that the above is true. Perhaps your methodology will help you find the. . . .
Some 4 digit numbers can be written as the product of a 3 digit
number and a 2 digit number using the digits 1 to 9 each once and
only once. The number 4396 can be written as just such a product.
Can. . . .