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The Best Card Trick?

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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Substitution Cipher

Find the frequency distribution for ordinary English, and use it to help you crack the code.

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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?

Substitution Transposed

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

Why do this problem?

Together with the Secondary Cipher Challenge, this problem provides a challenging follow-up for students who have worked on Substitution Cipher and Transposition Cipher.


Possible approach

As this problem is quite challenging, it could be offered as an extension for those students who have sailed through the easier codebreaking problems.

If a whole class is going to work on the problem, they could work in small groups and share out responsibility for checking different transposition arrangements for each likely substitution.

If a computer room is available, introduce students to the Cipher Challenge Toolkit and give them plenty of time to explore it and learn how to use the tools.


Possible extension

The Stage 5 Cipher Challenge offers a set of seven very difficult linked ciphers to crack.


Possible support

Spend plenty of time working on and discussing the separate Substitution and Transposition problems before trying this one.