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? Find the frequency distribution for ordinary English, and
use it to help you crack the code. Here is the start of a six-
part challenge. Can you get to the end and crack the final
message? Agent X is a secret agent in the field. She needs to
transmit enemy movements back to base. Her opportunities to send
messages are limited so she has to transmit the data as
accurately and efficiently as possible. To transmit the compass
direction of the enemy movements, she uses this diagram: Agent X
sent the message 0010 because the enemy were travelling North-
East. Unfortunately one of the digits was altered in
transmission so her base camp received the message 1010, South-
West, instead! Before reading on, you may wish to think of ways
of sending extra information to try to get the message through
even if a digit might get altered. One method of sending
communications is to include an ext