# Thread: I do not even know where to start (Mean and Stndrd Deviation probability problem)

1. ## I do not even know where to start (Mean and Stndrd Deviation probability problem)

The maximum snow load expected on a roof during the life of a domed stadium is a normally distributed random variable with mean = 50 lb/ft^2 and standard deviation of 8 lb/ft^2. What is the probability that the snow load will exceed 60 lb/ft^2 at some time?

2. ## Re: I do not even know where to start (Mean and Stndrd Deviation probability problem)

The maximum snow load expected on a roof during the life of a domed stadium is a normally distributed random variable with mean = 50 lb/ft^2 and standard deviation of 8 lb/ft^2. What is the probability that the snow load will exceed 60 lb/ft^2 at some time?
this is about as straightforward a probability problem as there could be. If you don't even know where to start you need to pay more attention in class or to your textbook.

Take your value, 60 lb/ft^2, normalize it according to the mean and deviation of your snow load distribution, 50 and 8 lb/ft^2, also known as finding it's z-score, and use the table of the CDF of the standard normal to find your probability.

Note it will be 1 - Pr[snow load < 60 lb/ft^2].

3. ## Re: I do not even know where to start (Mean and Stndrd Deviation probability problem)

Transform to a Z score $\displaystyle Z=\frac{X-\mu}{\sigma} = \frac{60-50}{8} = 1.25$

Now find $\displaystyle P(Z>1.25)$

4. ## Re: I do not even know where to start (Mean and Stndrd Deviation probability problem)

There's a good app for the normal distribution at
Standard Normal Distribution Table