# Standard deviation

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7. Assume that the midterm's scores X are normally distributed. Let X have a mean of 72 and a standard deviation of 12. Then answer the following three questions:

a. What is the probability of obtaining a score at least 90?

b. What is the probability of obtaining a score at most 75?

c. What is the probability of obtaining a score between 60 and 79?

https://brainmass.com/statistics/normal-distribution/standard-deviation-3633

#### Solution Preview

Cumulative Distribution Function

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<br>Normal with mean = 72.0000 and standard deviation = 12.0000

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<br> x P( X <= x )

<br> 90.0000 0.9332

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<br>SO Prob of at least 90 = 1 - .9332

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<br>Cumulative Distribution ...

$2.49