## Basic Probability Question Help

I need help with 2 questions:

1) In a shipment of 18 trucks to a local truck dealer, there are 4 trucks that don't have air conditioning. Assume you select 4 trucks at random.

What is the probability that two of the four don't have air conditioning?
What is the probability that two or fewer of the four don't have air conditioning?

I tried to use permutation for this problem, but I'm not sure if that is right or which numbers to use: n!/ (n-x)! or maybe n! (n-r)r!

2) The volume of a one-pound bag of coffee is normally distributed. Suppose you take a random sample of 15 one-pound bags of coffee. Find two values K sub L and K sub U such that the probability is 95% that the ratio of the sample standard deviation divided by the population standard deviation is between K sub L and K sub U.

I don't understand what the question is asking or what K sub L and U are to be? Can both these questions be done on excel? If so, what formula?

Thanks