# Binominal Distribution

#### ianhirst

##### New Member
For this kind of question would I be best using the Binominal Distribution equation?

So
(n!/X!(n-X)!) (p^X(1-p)^n-x)

Or would another probability method be preferred?

The question is below

It is found that 30% of Americans who exercise daily by running are men. A randomly selected group comprises of 20 people who exercise daily, with a certain number of men in the group. What is the approximate probability that there will be an exactly 15 males in the group?

#### Dragan

##### Super Moderator
For this kind of question would I be best using the Binominal Distribution equation?

So
(n!/X!(n-X)!) (p^X(1-p)^n-x)

Or would another probability method be preferred?

The question is below

It is found that 30% of Americans who exercise daily by running are men. A randomly selected group comprises of 20 people who exercise daily, with a certain number of men in the group. What is the approximate probability that there will be an exactly 15 males in the group?
Because the question is asking for an approximate probability - instead of an exact probability - just use a normal curve approximation.

#### asterisk

##### New Member
But, if they want exactly 15 males, not 15 or more, or 15 or less, I would go with Binomial.

$${{20}\choose{15}} * .3^{15} * .7^5$$

#### Dragan

##### Super Moderator
Yes, I agree.

However, that's not what's being asked for in the OP's question - i.e. an approximation