Table of Contents

• 1: Introduction
• The Law of OR
• 2: All Life's a Game
• 3: The Law of OR
• 4: Some Fine Print
• 5: What if you violate the fine print?
• The Law of AND
• 6: More game shows
• 7: What are the chances?
• 8: The Law of AND
• 9: More Fine Print
• 10: Examples of independent events
• 11: What if you violate the fine print?
• AND and OR together
• 12: Summary
• 13: Practice with dice
• 14: Practice with coins
• Biological Applications
• 15:What else can probability do?
• 16: To Curl or not to Curl
• 17: Surviving the Numbers Game
• 18: Gaining an Edge
• 19: Hanging on for Dear Life

Some Fine Print Relating to the Law of OR

Once again, The Law of OR says, if you need to know the probability that one thing OR another will take place, just add their separate probabilities.

Of course it's not (quite) that simple. Here's the fine print: the events in question have to be mutually exclusive. In other words, you will win one prize, but not two, or three, or four.

Here are some mutually exclusive events:

• Your friend is pregnant OR not pregnant;
  as we all know, there's no such thing as a little pregnant.
• Your mother offers you cake OR a brownie for dessert.
  You can't get both!
• You have one dollar. You can buy fries OR a donut OR a small milkshake,
  but after you buy one thing, your money's gone, you're out of luck.

Here are some non-mutually exclusive events:

• Your grandmother offers you cake OR a brownie OR both.
  But take both dear, you're too skinny!
• Your friend has a cold OR a flu OR maybe both,
  she looks so miserable.
• You just got paid, to celebrate you could get fries OR a donut OR a small milkshake
  OR any combination of the above.

 

Which of the following sets of choices are mutually exclusive?