there are 13 spades in a deck
1st card would be 13/52 probability of a spade
2nd card would be 12/51
3rd card would be 11/50
to find total probability, multiply all 3 together:
13/52 * 12/51 * 11/50 = 1716 / 132600
divide both sides by 156 to reduce the fraction to 11/850 probability
