# Codebreakers

Calling all maths detectives!

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

### Codebreakers

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

### Count the Digits

##### Age 5 to 11Challenge Level
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 ...

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

### Secret Number

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

### What Number?

##### Age 5 to 7 ShortChallenge Level
I am less than 25. My ones digit is twice my tens digit. My digits add up to an even number.

### Number Detective

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

### Coded Hundred Square

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

### Mystery Matrix

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

### Curious Number

##### Age 7 to 11Challenge Level
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

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