Having to do with standard deviation, and percent of scores. Please help me.

VaneB
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Homework Statement



The scores on an exam are normally distributed, with a mean of 77 and a standard deviation of 5. What percent of the scores are greater than 87?




Homework Equations





The Attempt at a Solution

I don't understand what it is exactly that I have to do to get the answer. Please Help!
 
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You'll need to use the probability density function or the cumulative distribution function for the normal distribution. Which one?
 

Thread 'Finding the nth roots of a complex number'

There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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