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Alice forgot the code to get into her computer. She knows it was a number with three digits, like 286 or 935. All she can remember is that the first digit is the second digit minus 3. The second digit is 4 times the third digit. And two of the digits are the same. Can you help Alice get into her computer?

Lavonne is testing a secret code with her friend Jack. First, she picks 3 different secret numbers between 1 and 9. Then she finds the sum of each pair of numbers. Lavonne wants to know if Jack can figure out the original secret numbers just from the sums?

If you’re sitting there twiddling your thumbs, see if you can decode this message. If you need a hint, you can always phone a friend! 3666882255533 443355544499 339987772

You’ve just received a secret coded message: AD, BA, BH, CE, DB, DI, EF You know it follows a pattern, but can you work out what pair of letters come next?

Learn the Caesar cipher, one of the oldest codes ever devised!

Written by Gabrielle Tramby In this activity you’ll do maths like a computer. It’s a bit tricky, so younger readers may want to read the ‘What’s Happening?’ section first.