title: Number of possible outcomes for 2 numbers given that one number is greater than the other
body: <p>I am trying to write an algorithm to calculate outcomes. But I need help with combinatorics.</p>
  
  <p>Suppose I have to choose 2 numbers from 1 to 10. 
  From the fundamental rule of counting, in the absence of any restriction, the number of possible outcomes is 10 * 10 = 100. (10 possible outcomes in choosing the first number x 10 possible outcomes in choosing the second).</p>
  
  <p>What is the number of possible outcomes given that the first number has to be greater than  the second number? </p>