Euler's Squares

Euler found four whole numbers such that the sum of any two of the numbers is a perfect square...

Odd Differences

The diagram illustrates the formula: 1 + 3 + 5 + ... + (2n - 1) = n² Use the diagram to show that any odd number is the difference of two squares.

Substitution Cipher

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

What would you need to multiply by to do the same job as calculating $10\%$ and then adding it on ?