Standard deviation problem

• Apr 21st 2009, 01:11 PM
Joseph Smith
Standard deviation problem

The average starting salary for this year's graduates at a large university is $20,000 with a standarad deviation of$8,000. Furthermore, it is known that the starting salaries are normally ditributed.

a. What is the probability that a randomly selected LU graduate will have a starting salary of at least 30,400?

b. Individuals with starting salaries of less than $15,600 receive a low income tax break. What percentage of the graduate will receive tax break? c. What are the minimum and the maximum starting salaries of the middle 95% of the LU graduates? d. If 189 of the recent graduates have salaries of at least$32,240, how many students graduate this year from the university?
• Apr 21st 2009, 09:10 PM
matheagle
I'll do the first one

$P( X> 30,400)=P\biggl( {X-20,000\over 8000}> {30,400-20,000\over 8000}\biggr)=P(Z>1.3)\approx .0968$.

The next one is $P( X< 15,600)$...