Think of a two digit number, reverse the digits, and add the numbers together. Something special happens...
The number 27 is special because it is three times the sum of its digits 27 = 3 (2 + 7). Find some two digit numbers that are SEVEN times the sum of their digits (seven-up numbers)?
Consider all two digit numbers (10, 11, . . . ,99). In writing down
all these numbers, which digits occur least often, and which occur
most often ? What about three digit numbers, four digit numbers. . . .
Pick the number of times a week that you eat chocolate. This number must be more than one but less than ten.
Multiply this number by 2. Add 5 (for Sunday). Multiply by 50... Can you explain why it. . . .
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
32 x 38 = 30 x 40 + 2 x 8; 34 x 36 = 30 x 40 + 4 x 6; 56 x 54 = 50
x 60 + 6 x 4; 73 x 77 = 70 x 80 + 3 x 7 Verify and generalise if
Replace each letter with a digit to make this addition correct.
A car's milometer reads 4631 miles and the trip meter has 173.3 on
it. How many more miles must the car travel before the two numbers
contain the same digits in the same order?
Exploring the structure of a number square: how quickly can you put the number tiles in the right place on the grid?
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.
A three digit number abc is always divisible by 7 when 2a+3b+c is divisible by 7. Why?
Take any four digit number. Move the first digit to the 'back of
the queue' and move the rest along. Now add your two numbers. What
properties do your answers always have?
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?
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.
Use two dice to generate two numbers with one decimal place. What happens when you round these numbers to the nearest whole number?
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?
What happens when you round these three-digit numbers to the nearest 100?
What happens when you round these numbers to the nearest whole number?
This 100 square jigsaw is written in code. It starts with 1 and
ends with 100. Can you build it up?
A game to be played against the computer, or in groups. Pick a 7-digit number. A random digit is generated. What must you subract to remove the digit from your number? the first to zero wins.
This is a game in which your counters move in a spiral round the snail's shell. It is about understanding tens and units.
Investigate which numbers make these lights come on. What is the smallest number you can find that lights up all the lights?
This activity involves rounding four-digit numbers to the nearest thousand.
A church hymn book contains 700 hymns. The numbers of the hymns are
displayed by combining special small single-digit boards. What is
the minimum number of small boards that is needed?
How many solutions can you find to this sum? Each of the different letters stands for a different number.
Watch our videos of multiplication methods that you may not have met before. Can you make sense of them?
Find the sum of all three-digit numbers each of whose digits is
This article, written for teachers, looks at the different kinds of
recordings encountered in Primary Mathematics lessons and the
importance of not jumping to conclusions!
The number 3723(in base 10) is written as 123 in another base. What
is that base?
There are nasty versions of this dice game but we'll start with the nice ones...
Who said that adding, subtracting, multiplying and dividing
couldn't be fun?
Start by putting one million (1 000 000) into the display of your
calculator. Can you reduce this to 7 using just the 7 key and add,
subtract, multiply, divide and equals as many times as you like?
Each child in Class 3 took four numbers out of the bag. Who had
made the highest even number?
Powers of numbers behave in surprising ways. Take a look at some of these and try to explain why they are true.
Using balancing scales what is the least number of weights needed
to weigh all integer masses from 1 to 1000? Placing some of the
weights in the same pan as the object how many are needed?
You have two sets of the digits 0 – 9. Can you arrange these
in the five boxes to make four-digit numbers as close to the target
numbers as possible?
Nowadays the calculator is very familiar to many of us. What did
people do to save time working out more difficult problems before
the calculator existed?
In the multiplication calculation, some of the digits have been replaced by letters and others by asterisks. Can you reconstruct the original multiplication?
Follow the clues to find the mystery number.
How many six digit numbers are there which DO NOT contain a 5?
Find the values of the nine letters in the sum: FOOT + BALL = GAME
Have a go at balancing this equation. Can you find different ways of doing it?
What do the digits in the number fifteen add up to? How many other
numbers have digits with the same total but no zeros?
Can you complete this calculation by filling in the missing numbers? In how many different ways can you do it?
Take the numbers 1, 2, 3, 4 and 5 and imagine them written down in
every possible order to give 5 digit numbers. Find the sum of the
How many positive integers less than or equal to 4000 can be
written down without using the digits 7, 8 or 9?
Can you work out some different ways to balance this equation?
Can you substitute numbers for the letters in these sums?
Can you replace the letters with numbers? Is there only one
solution in each case?
The Scot, John Napier, invented these strips about 400 years ago to
help calculate multiplication and division. Can you work out how to
use Napier's bones to find the answer to these multiplications?