Statistics

I'm stumped on this question.
A teacher informs her history class that a test is very difficult, but the grades would be curved. Scores for the test are normally distributed with a mean of 25 and a standard deviation of 5. If the grades are curved according to the following scheme, find the numerical limits for each grade.
A: Top 10%
B: Scores above the bottom 70% and below the top 10%
C: Scores above the bottom 30% and below the top 30%
D: Scores above the bottom 10% and below the top 70%.
F: Bottom 10%

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  1. Z = (score-mean)/SD

    Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions and their Z scores. Insert the values into equation above to find the scores.

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