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You'll Flip
Independent Events

 

 When people try to tell how likely it is that something will happen,

 they often use percents.
 
 Like when TV weather types try to predict if it will rain tomorrow.
 
 A 100 percent chance of rain tomorrow means that it WILL rain tomorrow.
 
 A zero percent chance of rain tomorrow means that it WILL NOT rain tomorrow.
 
 A fifty percent chance of rain tomorrow means
 that there is an equal chance that it WILL or WILL NOT rain tomorrow.
 
 Some people call an equal chance between two things a coin toss.
 
 Take a coin. Flip it end over end in the air. 
 If the coin and the flip are fair, 
 there is an equal chance that either side will end up on top.
 
 Once again, there is an equal chance that either side
 will end up on top any time the coin is flipped.
 
 No matter what happened on the last flip or the last hundred flips,
 each flip is a whole new ballgame.
 
 Examples:
 1) A penny comes up heads the last ten times that you flipped it.
 
 What is the chance that it will come up heads on the next flip?
 

 FIFTY PERCENT

 
 2) The same penny has come up tails the last ten times that you have flipped it.
 
 What is the chance that it will come up heads this time?
 

 FIFTY PERCENT

 
 3) The last six flips of the penny have come up 
 HEADS - TAILS - HEADS - TAILS - HEADS - TAILS.
 What is the chance that it will come up heads on the next flip?
 

 FIFTY PERCENT

 
 So great. Any time that you flip a coin it has an equal chance
 of coming up heads or coming up tails.
 It doesn't make any difference what happened 
 on any flip that came before the current one.
 The chance of the coin coming up heads on any flip is
 

 FIFTY PERCENT

 
 Because each flip stands on it's own 
 and does not depend on what happened before,
 statistics types call coin flips
 

 INDEPENDENT EVENTS

 
 Lot's of things that happen over and over are independent events.
 
 Rolls of a pair of dice are independent events.
 
 What number comes up on a roulette wheel each time is an independent event.
 
 If the situation is the same after the event as it was before the event,
 the events are probably independent.
 
 There are also lots of events that are NOT independent.
 
 They do depend on what has happened before.
 If it is 100 degrees outside today, it is not likely it will snow here tomorrow.
 If the first card you are dealt from a regular deck is the king of hearts,
 it's not very likely the second will be the king of hearts too.
 
 We call these dependent events.
 

   copyright 2005 Bruce Kirkpatrick

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