Probability questions for statistics

A set of final examination grades in a course is normally distributed with a mean of 73 and a standard deviation of 8.

1. What is the probability of getting a grade below 91 on the exam?
2. What is the probability that a student scored between 65 and 89?
3. If the professor grades on a curve (gives A’s to the top 10% of the class, regardless of the score), are you better off with a grade of 81 on this exam or a grade of 68 on a different exam, where the mean is 62 and the standard deviation is 3? Explain why.
• Welcome to the site. This looks like homework or an exam question. If it is, please add the self-study tag. – Peter Flom - Reinstate Monica Oct 27 '13 at 18:08
• We welcome questions like this, @Megan Brown, but we treat them differently (see our help page). Please tell us what you understand & have tried already, & we'll provide some hints to help get you unstuck. – gung - Reinstate Monica Oct 27 '13 at 18:28
• I am trying to calculate the z-score. Using the formula z= y-mean / standard deviation. Can't find our what value to use for y – user31966 Oct 27 '13 at 18:30