Probability

Probability

How to solve the basic probability problems: definition, examples, and their solutions. (including geometric probability)

Definition

P(want) = n(want)/n(total).

The probability is
(number of wanted ways) / (number of total ways).

Example 1

A bag is filled with 15 colored and shaped cards. In selecting a card without looking, find the probability of selecting a gray card.

There are 8 ways to select a gray card.

And there are 15 ways to select a card.

So the probability of selecting a gray card is 8/15.

Example 2

A bag is filled with 15 colored and shaped cards. In selecting a card without looking, find the probability of selecting a circle card.

There are 3 ways to select a circle card.

And there are 15 ways to select a card.

So the probability of selecting a circle card is 3/15, 1/5.

Example 3: Geometric Probability

For the given dartboard, when throwing a dart once, find P(colored).

The total area is 12.

And the colored area is 3.

So the probability of hitting the colored area is 3/12, 1/4.