The mean of a normal probability distribution is 60; the standard deviation is 5. a. About what

Question:

The mean of a normal probability distribution is 60; the standard deviation is 5.
a. About what percent of the observations lie between 55 and 65?
b. About what percent of the observations lie between 50 and 70?
c. About what percent of the observations lie between 45 and 75?

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