# help

#### 1NAMILL

##### New Member
I am having trouble with the folowing question:

Use the Poisson Distribution to find the indicated probability.

A computer salesman averages 1.5 sales per week. Use the Poisson distribution to find the probability that in a randomly selected week the number of computers sold is 2.

I'm not sure how to find the mean. Do I divide 2 with 7 days in a week or the # of sales (1.5) in a week (7)?

I really need help.

#### 1NAMILL

##### New Member
Now this is where I get lost. If the question is:

A computer salesman averages 1.5 sales per week. Use the Poisson distribution to find the probability that in a randomly selected week the number of computers sold is 2.

And the mean is 1.5. How can I find the ansswer using the Poisson distribution? I get lost with the equation. What is x? Is it 2 for the number of computers sold or is it 7 for the number of days in a week?

#### 1NAMILL

##### New Member
Never mind. I figured it out. Thanks

#### 1NAMILL

##### New Member
I'm stuck. the question is:

The scores on a certain test are normally distributed with a mean score of 65 and a standard deviation of 2. What is the probability that a sample of 90 students will have a mean score of at least 65.2108?

I tried to use the formula for the standard normal distribution. However, I'm not sure what to use as "X" and I'm not sure which "mean" I should use. I do know that the sd is 2. Please help

#### 1NAMILL

##### New Member
Here's one more.

Use the given degree of confidence and sample data to find a confidence interval for the population standard deviation . Assume that the population has a normal distribution.

The amounts (in ounces) of juice in eight randomly selected juice bottles are:
15.1 15.8 15.2 15.4 15.4 15.6 15.0 15.6

Find a 98 percent confidence interval for the population standard deviation.
I'm not sure what to do here. Do I find need to find the mean? (I know it's 15.3925). However, I don't know what to do next?

#### JohnM

##### TS Contributor
Standard deviations follow a chi-square distribution.....

Look at my post in the Examples section entitled "Computing Confidence Intervals" - there's an example for the std dev