Factors, Multiples and Primes

Counting Cogs

KS 2 & 3 Challenge Level:

Challenge Level:2 Challenge Level:2

Which pairs of cogs let the coloured tooth touch every tooth on the other cog? Which pairs do not let this happen? Why?

Factors and Multiples Game

KS 2, 3 & 4 Challenge Level:

Challenge Level:1

A game in which players take it in turns to choose a number. Can you block your opponent?

Sieve of Eratosthenes

KS 3 Challenge Level:

Challenge Level:1

Follow this recipe for sieving numbers and see what interesting patterns emerge.

Factors and Multiples Puzzle

KS 3 Challenge Level:

Challenge Level:1

Using your knowledge of the properties of numbers, can you fill all the squares on the board?

Reversible Primes

KS 3 Short Challenge Level:

Challenge Level:1

How many two-digit primes are there between 10 and 99 which are also prime when reversed?

Divisible Digits

KS 3 Short Challenge Level:

Challenge Level:1

Can you find the missing digits, given that the number is divisible by 3, 4, 5 and 6?

American Billions

KS 3 Challenge Level:

Challenge Level:1

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...

Multiple Surprises

KS 3 Challenge Level:

Challenge Level:1

Sequences of multiples keep cropping up...

How Much Can We Spend?

KS 3 Challenge Level:

Challenge Level:1

A country has decided to have just two different coins, 3z and 5z coins. Which totals can be made? Is there a largest total that cannot be made? How do you know?

Dozens

KS 3 Challenge Level:

Challenge Level:1

Do you know a quick way to check if a number is a multiple of two? How about three, four or six?

What Numbers Can We Make?

KS 3 Challenge Level:

Challenge Level:1

Imagine we have four bags containing a large number of 1s, 4s, 7s and 10s. What numbers can we make?

Red Card Blue Cardlive

KS 3 Short Challenge Level:

Challenge Level:2 Challenge Level:2

Can you arrange the red and blue cards so that the rules are all followed?

Counting Factors

KS 3 Challenge Level:

Challenge Level:2 Challenge Level:2

Is there an efficient way to work out how many factors a large number has?

Stars

KS 3 Challenge Level:

Challenge Level:2 Challenge Level:2

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?

Leap Monday

KS 3 Short Challenge Level:

Challenge Level:3 Challenge Level:3 Challenge Level:3

Can you find the next time that the 29th of February will fall on a Monday?

Differences

KS 3 Challenge Level:

Challenge Level:3 Challenge Level:3 Challenge Level:3

Can you guarantee that, for any three numbers you choose, the product of their differences will always be an even number?

Funny Factorisation

KS 3 Challenge Level:

Challenge Level:3 Challenge Level:3 Challenge Level:3

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 you find the factors?

Factors, Multiples and Primes - Short Problems

KS 3 & 4

A collection of short Stage 3 and 4 problems on factors, multiples and primes.

Gabriel's Problem

KS 3 & 4 Challenge Level:

Challenge Level:1

Gabriel multiplied together some numbers and then erased them. Can you figure out where each number was?

Power Mad!

KS 3 & 4 Challenge Level:

Challenge Level:2 Challenge Level:2

Powers of numbers behave in surprising ways. Take a look at some of these and try to explain why they are true.

Take Three from Five

KS 3 & 4 Challenge Level:

Challenge Level:2 Challenge Level:2

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?

Product Sudoku

KS 3, 4 & 5 Challenge Level:

Challenge Level:1

The clues for this Sudoku are the product of the numbers in adjacent squares.

Divisibility Tests

KS 3, 4 & 5

This article takes the reader through divisibility tests and how they work. An article to read with pencil and paper to hand.

Filling the Gaps

KS 4 Challenge Level:

Challenge Level:2 Challenge Level:2

Which numbers can we write as a sum of square numbers?

Expenses

KS 4 Challenge Level:

Challenge Level:2 Challenge Level:2

What is the largest number which, when divided into 1905, 2587, 3951, 7020 and 8725 in turn, leaves the same remainder each time?

Adding a Square to a Cube

KS 4 Short Challenge Level:

Challenge Level:3 Challenge Level:3 Challenge Level:3

If you take a number and add its square to its cube, how often will you get a perfect square?