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## 'Code Breaker' printed from http://nrich.maths.org/

Many modern codes are based on two very large prime numbers
multiplied together.

This problem is based on a code using two different prime
numbers less than 10. These two primes have been multiplied
together and the resulting number has been used to shift the
alphabet forward to new letters, assuming that A is at position 1,
B at position 2 etc. For example, if the two prime numbers were 2
and 3, then to make the code, the alphabet would be shifted forward
by 6 places. A would become G, B shifts to H and so on.

Which way will you need to shift the letters to decode?

When you have deciphered the code, there will be one word which
will remain coded. You can decipher this word by adding the two
prime numbers together and shifting the letters again.

Can you find the doubly coded word in this sentence?

JZF SLGP FUDFNHG TE

You may want to use this interactive code breaker to help you.
Shift the red letters by clicking on the red F (forwards) and B
(backwards) and then you'll need to use the blue letters in the
same way to decipher the doubly coded word.

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