Probability: A and B

How to find the probability P(A and B): 1 example, and its solution.

Example

Example

Solution

Set A as
picking an odd number from 1 to 10.
{1, 3, 5, 7, 9}

Set B as
picking a prime number from 1 to 10.
{2, 3, 5, 7}

Then [A and B] is,
write the numbers in both A and B,
{3, 5, 7}.

The number of {3, 5, 7} is 3.
n(A and B) = 3

The number of [1 ~ 10] is 10.
n(S) = 10

Then P(A and B) = 3/10.

Probability

So 3/10 is the answer.