Explained Euclid's algorithm for finding the greatest common divisor of
two numbers, and used it to find the inverse of some number n modulo m.
An application of modular arithmetic to <a href="https://en.wikipedia.org/wiki/International_Bank_Account_Number">IBAN bank numbers</a> was explained.<br>
<br>
Take a look at <a href="http://www.youtube.com/watch?v=fz1vxq5ts5I">this
clip</a>
for another
example of using the Euclidean algorithm to find the inverse of a
number in modular arithmetic. <br>
      <br>
For more background on modular arithmetic take a look at the wikipedia
page <a href="http://en.wikipedia.org/wiki/Modular_arithmetic">here</a>.
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See Section 5.4 of Lawson's book (available via Blackboard) for a rigorous introduction to, and further examples of,  Euclid's algorithm.