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### Defining Probability

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Date: 4/30/96 at 21:42:22
From: Gary L Knox
Subject: Probability

We got into quite a disagreement and would like another qualified
opinion.  It relates to the definition of probability.  Our text says
the probability of an event is a number between 0 and 1.  One person
thinks probabilities can be written only as a number from 0 to 1 like
.732, etc.  Another person says probabilities may be written as
percents.

Our question... is a probability number equal to a percent?
Is it correct to say the probability is 42 percent, the way they do on
the weather, or are they using sloppy wording?

Gary
```

```
Date: 5/1/96 at 15:47:48
From: Doctor Ethan
Subject: Re: Probability

In my opinion, percents are a perfectly valid way to represent a
probability.

In essence both probabilities and percents measure ratios of
occurrences, and so they both seem like very natural ways to represent
the same concepts.

In my experience, decimals are the most computationally efficient way
to represent probabilities but I can think of cases where I would
rather use fractions or percents.

I think that the biggest problem (and maybe this is big enough) is
linguistic awkwardness.

Percents are usually used in a sentence like this:

She got 93% of the answer right.
(This is not a probability measure.)

However, I think that we also might say

She has a 93% chance of getting the next problem right.
(This is a probability measure.)

So I guess I would say that although there may be a pedagogical reason
to keep the notation distinct, these are in fact both ways of
expressing ratios of values, and therefore could be used
interchangeably with consistency.

-Doctor Ethan,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
Associated Topics:
High School Definitions
High School Probability
Middle School Definitions
Middle School Probability

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