Statistics question: need help on how to figure this out?

Question

The professor has determined that the scores in his course are distributed with a mean of 75 and a standard deviation of 5. He announces that the top 10% of the scores will earn a "A". What is the lowest score a student can receive and still get A?

Answer 1

I'm not sure what all the steps are, but one thing you'll need to do is find how many standard deviations 80% of the scores are from the mean. 10% of the scores fall above that range, and 10% fall below.

I wanna say that there is a chart that tells you how many standard deviations 80% of values are in a normally distributed population(it's probably a number between 2 and 3), but I'm not sure. The chart would be inside the cover in your textbook, or in the appendix...Anyway you would take that number, multiply it by 5, then add it to 75 to get your answer.

I believe the answer is the maximum score in that 80% range (or the next whole number rounded up) .

Answer 2

Assuming that the scores are normally distributed...
Z = (x - µ)/σ Where Z is the standard normal variate for the standard normal distribution.
In this case Z = +1.28 for 90% of the standard normal distribution.
Then, 1.28 = (X - 75)/5
Solve for X:
X = 75 + 1.28(5) = 81.4

Answer 3

I haven't even formulated how much work that will take but I'm not getting the grades for it and so I'm not doing it.

I have studied SD standard deviation, Bell Curves, Pearson's Correlation, Spearman's Correlation, etc but I'm just not doing it. I got well above A+ in that maths class, but just aint doing it honey. Lol.

And I studied psychology [where we'd need SD to check if our hypotheses are right or not] but just aint doing it..... Byse bye.

I admire your sheer nerve, though.