# Find a probability

• Dec 6th 2009, 01:17 PM
cechmanek32
Find a probability
Here is the question. It's probably very simple and I just can't figure it out:

A statistics professor plans classes so carefully that the lengths of her classes are uniformly distributed between 50.0 and 52.0 minutes. Find the probability that the class runs less than 50.25 minutes.

Does this have something to do with a z-score? I know probability=percent (at least thats what my teacher says) but I'm not sure how to work this one...and it seems like it should be so simple.

Thank you!!
• Dec 6th 2009, 01:23 PM
TheEmptySet
Quote:

Originally Posted by cechmanek32
Here is the question. It's probably very simple and I just can't figure it out:

A statistics professor plans classes so carefully that the lengths of her classes are uniformly distributed between 50.0 and 52.0 minutes. Find the probability that the class runs less than 50.25 minutes.

Does this have something to do with a z-score? I know probability=percent (at least thats what my teacher says) but I'm not sure how to work this one...and it seems like it should be so simple.

Thank you!!

If the R.V is uniform then it has a density function

$f(x)=\begin{cases} \frac{1}{2} \text{ if } x \in [50,52] \\
0 \text { otherwise }\end{cases}$

$\int_{50}^{50.25}\frac{1}{2}dx=\frac{1}{2}\cdot \left( 50.25-50\right)=\frac{1}{8}$
• Dec 6th 2009, 01:25 PM
pickslides
Quote:

Originally Posted by cechmanek32
Here is the question. It's probably very simple and I just can't figure it out:

A statistics professor plans classes so carefully that the lengths of her classes are uniformly distributed between 50.0 and 52.0 minutes. Find the probability that the class runs less than 50.25 minutes.

This distribution implies each value has the same probability of occuring.

Quote:

Originally Posted by cechmanek32
Does this have something to do with a z-score? Thank you!!

This implies when the distribution is normal.

Quote:

Originally Posted by cechmanek32
I know probability=percent (at least thats what my teacher says) but I'm not sure how to work this one...and it seems like it should be so simple.

Thank you!!

This is good advice for this question
• Dec 8th 2009, 07:26 PM
cechmanek32
Find A Probability (Question 2)
I would like to see if someone could check me on this one:

A statistics professor plans classes so carefully that the lengths of her classes are uniformly distributed between 50.0 and 52.0 minutes. Find the probability that the class runs greater than 51.25 minutes.

Am I correct in saying 0.375? If not, then I need help in figuring out how to solve this one again. Thanks!!
• Dec 9th 2009, 01:23 AM
ANDS!