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We use ratios
to show how likely, or unlikely, an outcome might be.
This
ratio is called the probability.
For example,
the probability of getting heads on the toss of a penny is the ratio
 . Heads
is one of two possible outcomes when a penny is tossed. |
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Our ratio for
probability can be thought of as:
Ratios are most
often expressed in the form of a fraction. Fractions, however, can
also be expressed as decimals or percents. So probabilities may be
expressed as fractions, decimals or percents.
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As the chart
on the left
shows, probabilities range from 0 to 1.
If an event is
impossible
and will never occur, the probability is 0.
If an event is
absolutely certain to occur, the probability is 1.
Otherwise, the
value of a probability is between 0 and 1. |
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Events that are
likely to occur have a
probability greater than 0.5.
Events that are not likely to occur
have a probability less than 0.5. |
While probability
was originally developed to deal with gaming techniques, it is used today
in a wide range of applications. Even common sayings reflect the
concept of probability:
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Someone may say "Don't hold your breath" when you are waiting
for something to happen. What is the person implying about
the probability that the event will occur in the near future? |
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ANSWER: This
statement implies that you may die holding your breath waiting for this
event to occur.
Obviously, the probability of the event occurring in the near future, is extremely
low, if not impossible.
Example:
A fair die is rolled, and the outcome noted.
Determine whether each of the following outcomes is: certain to
happen, certain not to happen, likely to happen,
likely to not happen.
• rolling a 2
• rolling a number less than 3
• rolling a 7
• rolling a number less than 10
• rolling a number greater than 1
• rolling a factor or 6
(1,2,3,6)
• rolling a number that is an
integer
• rolling a negative number |
• probability = 1/6 likely to not happen
• probability = 1/6 + 1/6 = 2/6 likely not to
happen
• not possible - certain not to happen
• certain to happen
• probability = 5/6 likely to happen
• probability = 4/6 likely to happen
• certain to happen
• certain not to happen |
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