Finding and Interpreting the Odds of Success
Date: 08/04/2004 at 12:41:48 From: Jimmy Subject: Odds What does it mean when you see odds expressed as 5 to 1 (or 5:1)? How do you calculate such odds?
Date: 08/06/2004 at 12:55:57 From: Doctor Achilles Subject: Re: Odds Hi Jimmy, Thanks for writing to Dr. Math. Usually, odds of something happening are given as X-to-1. If the odds of something happening are 1-to-1, that means there is an equal chance of the thing happening as not. So the odds of getting heads on a coin toss are 1-to-1. If the odds are 2-to-1, that means there is twice as good a chance that the thing WON'T happen as that it will. If I roll a single 6- sided die, the odds of me getting a 5 or 6 are 2-to-1 since I'm twice as likely to fail as to succeed. If the odds are 1-to-2, that means there is twice as good a chance that the thing will happen as that it won't. If I roll a die, the odds of me getting a 3, 4, 5, or 6 are 1-to-2. To calculate odds you first count up the number of ways the thing can not happen. With the die, there are 4 ways I can not get a five or six (if I get a one, two, three, or four). Then you count up the number of ways the thing can happen. For rolling a die, there are 2 ways I can get a five or six. Then you put the number of ways you can fail to get your outcome (4) as the first number and the number of ways you can succeed (2) as the second number. So the odds are 4- to-2. Once you have done that, you can divide both numbers by anything you like. Let's divide them both by 2 so it is a little simpler. That makes the odds 2-to-1. If you need your odds to be expressed as X-to-1, then you just divide by the second number. So, the odds of getting a 3, 4, 5, or 6 on a die are 1-to-2 or 0.5-to-1. Hope this helps. If you have other questions or you'd like to talk about this some more, please write back. - Doctor Achilles, The Math Forum http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994-2013 The Math Forum