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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?

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Secret Transmissions

How can Agent X transmit data on a faulty line and be sure that her message will get through?

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Secondary Cipher Challenge Part 1

Here is the start of a six-part challenge. Can you get to the end and crack the final message?

Substitution Cipher

Stage: 3 and 4 Challenge Level: Challenge Level:1

Start by performing a frequency analysis on some selected text to see which letters appear most often. It is better to use longer texts, as a short text might have an unusual distribution of letters, like the "quick brown fox..." mentioned in the problem.

 

The toolkit allows you to change a pair of letters quickly and see the effect it has on the message. Alternatively, you could use Word's "Find and Replace" feature, with the 'Match Case' option, to change one letter at a time. You can distinguish between the coded message and the deciphered letters by using lower case for the coded message and replacing each letter by the upper case letter you think it represents.

 

The whole message has been encoded by switching pairs of letters.
For example, B and P have been switched so that every P is replaced by B, and every B replaced by P.