NUMBER OF THINGS YOU ARE LOOKING FOR PROBABILITY =  TOTAL NUMBER OF THINGS
Example  Problem  Answer  

1  What is the probability of a flipped coin turning up heads? 
because there is 1 head and the coin has 2 sides.  
2  What is the probability of pulling, at random, the ace of spades out of a deck of 52 cards? 
because there is only 1 ace of spades and there are 52 cards in the deck.  
3  What is the probability of drawing any ace out of a deck of 52 cards?  because there 4 aces in a deck of 52 cards.  
4  What is the probability of drawing a red marble out of a bag containing 2 red marbles and 5 blue marbles? 
