This big box adds something to any number that goes into it. If you know the numbers that come out, what addition might be going on in the box?
Shapes are added to other shapes. Can you see what is happening? What is the rule?
Here's a very elementary code that requires young children to read a table, and look for similarities and differences.
A case is found with a combination lock. There is one clue about the number needed to open the case. Can you find the number and open the case?
Letters have different values in Scrabble - how are they decided upon? And would the values be the same for other languages?
Can you follow the rule to decode the messages?
Find the frequency distribution for ordinary English, and use it to help you crack the code.
Time for a little mathemagic! Choose any five cards from a pack and show four of them to your partner. How can they work out the fifth?
Can you work out what size grid you need to read our secret message?
Here is the start of a six-part challenge. Can you get to the end and crack the final message?
Substitution and Transposition all in one! How fiendish can these codes get?
How can Agent X transmit data on a faulty line and be sure that her message will get through?
In 'Secret Transmissions', Agent X could send four-digit codes error free. Can you devise an error-correcting system for codes with more than four digits?
Is the regularity shown in this encoded message noise or structure?
Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?