# Normal distribution problem

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• Oct 9th 2011, 11:54 PM
brodydino
Normal distribution problem
Been having a hard time with this problem, can anyone help out?

Each year, thousands of college seniors take the Graduate Record Examination (GRE). Assume the scores are transformed so they have a mean of 600 and a standard deviation of 150. Furthermore, the scores are known to be normally distributed. Determine the percentage of students that score:
a. Between 650 and 825
b. 475 or greater
c. Below 750
d. Either less than 750 or more than 800
• Oct 10th 2011, 12:15 AM
mr fantastic
Re: Normal distribution problem
Quote:

Originally Posted by brodydino
Been having a hard time with this problem, can anyone help out?

Each year, thousands of college seniors take the Graduate Record Examination (GRE). Assume the scores are transformed so they have a mean of 600 and a standard deviation of 150. Furthermore, the scores are known to be normally distributed. Determine the percentage of students that score:
a. Between 650 and 825
b. 475 or greater
c. Below 750
d. Either less than 750 or more than 800

What have you tried? Where are your stuck. Have you reviewed your class notes and textbook for similar examples?
• Oct 10th 2011, 12:30 AM
brodydino
Re: Normal distribution problem
The farthest I got on A is this:

650-600/150= 0.33
825-600/1500= 1.5

Then I got their z scores, 0.6293 and 0.9332... don't know where to go from that
• Oct 10th 2011, 12:10 PM
mr fantastic
Re: Normal distribution problem
Quote:

Originally Posted by brodydino
The farthest I got on A is this:

650-600/150= 0.33
825-600/1500= 1.5

Then I got their z scores, 0.6293 and 0.9332... don't know where to go from that

Have you been taught to get probability from z-scores using tables? If so, the next step is to review how to use those tables (see your class notes or textbook). Note: The answer to (A) is

$\Pr(0.6293 < Z < 0.9332) = \Pr(Z < 0.9332) - \Pr(Z < 0.6293) = ....$