
Increase in the payments
Assuming that an increase in the parent payments follows a normal distribution with an average of 275 and with standard deviation of 250, answer the following questions:
a) Calculate the probability that parent payments in a randomly chosen day care center rise by something between 250 and 270
b) Calculate the probability that average parent payments in 15 randomly chosen day care centers increase by not more than 250 on average

You did not say where you are stuck, so i'll assume you only need the first step.
step 1: Standardise the variable

I don't know how to do this all. I don't understand statistics at all.
I will be doing this questions in Hypostat program so the most important for me is which kind of test (Test of the mean from one sample, Test the difference in the mean from 2 samples, Test for normality, Probability distributions and so on) should I use