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									Probability and Odds
     PSSA Unit
   When the weather channel
    predicts that the chance of
    rain for the next day is 70%, it
    is telling us that the likelihood
    for this precipitation to occur is
    7 chances out of 10.
        What is Probability?
•   Probability is a numerical measure
    indicating the chance or likelihood
    for a particular event to occur.
* It is usually expressed as a ratio
  namely by a fraction, decimal, or
   When we toss a coin in the air, it
    is equally likely that it will land
    heads up as tails up. Therefore,
    the chance that this coin will land
    heads up is one out of two, or 1/2.
   The set of all the possible outcomes
    of a given experiment is called the
    sample space.

   Probability of an event =
           number of favorable events
             total number of events
   A typical dice has 6 sides. Each side
    contains a number from 1-6.
   If you roll a die, what is the probability of
          1. A 4?
          2. An odd number?
          3. A number less than 3?
          4. A number more than 6?
   We said that the probability of rolling
    a 4 is 1/6.
   If we roll a die 30 times, how many
    times am I likely to get a 4?

             30 g  5 times
1. A 2, in 60 rolls.

2. An odd number, in 100 rolls.

3. A number less than 3, in 300 rolls.
Suppose the 8 letters of the words HOT
COCOA are written on cards, then
shuffled. If a card is chosen at random, the
probability that it will contain the letter 0 is
_____. What is the probability that it will

The letter C?
A vowel?
A letter in the word CHOCOLATE?
   Probability is often expressed
    in terms of “odds”.

     Odds in favor of an event 
      number of favorable outcomes
     number of unfavorable outcomes
   There are 12 colored marbles in a
    bag, and 3 of them are blue. What
    are the odds for drawing a blue
    marble from the bag?

 number of favorable outcomes  3 1
                               
number of unfavorable outcomes 9 3
What are the odds that you will win the
 prize if you hold 50 raffle tickets of
 the 1500 tickets sold at a charity
 number of favorable outcomes   50   1
                                  
number of unfavorable outcomes 1450 29
   A spinner has a circle with twelve
    numbers each numbered 1-12. What are
    the odds that the pointer stops on the first
    spin by a number divisible by 4?
   Numbers divisible by 4 include: 4,8, and
                 3 1
                    or 1 : 3
                 9 3

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