List

Codebreakers

Calling all maths detectives!

Can you solve the mysteries hidden in our carefully selected NRICH tasks?

Codebreakers
article

Codebreakers

This article for Primary and Secondary teachers is all about the mathematics behind solving puzzles, unravelling mysteries and breaking codes.
Count The Digits
problem
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Count The Digits

Age
5 to 11
Challenge level
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In this investigation we are going to count the number of 1s, 2s, 3s etc in numbers. Can you predict what will happen?
I Like ...
problem
Favourite

I Like ...

Age
5 to 7
Challenge level
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Mr Gilderdale is playing a game with his class. What rule might he have chosen? How would you test your idea?
Secret Number
problem
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Secret Number

Age
5 to 7
Challenge level
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Annie and Ben are playing a game with a calculator. What was Annie's secret number?
What number?
problem

What number?

Age
5 to 7
Challenge level
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I am less than 25. My ones digit is twice my tens digit. My digits add up to an even number.
Magnifying glass
problem
Favourite

Number Detective

Age
5 to 11
Challenge level
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Follow the clues to find the mystery number.

Coded hundred square
problem
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Coded hundred square

Age
7 to 11
Challenge level
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This 100 square jigsaw is written in code. It starts with 1 and ends with 100. Can you build it up?
Mystery Matrix
problem
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Mystery Matrix

Age
7 to 11
Challenge level
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Can you fill in this table square? The numbers 2 -12 were used to generate it with just one number used twice.
Curious number
problem
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Curious number

Age
7 to 11
Challenge level
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Can you order the digits from 1-3 to make a number which is divisible by 3 so when the last digit is removed it becomes a 2-figure number divisible by 2, and so on?

Satisfying Four Statements
problem
Favourite

Satisfying Four Statements

Age
7 to 11
Challenge level
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Can you find any two-digit numbers that satisfy all of these statements?