12.South Dakota Speeds. The National Motorists Association reports that, in South Dakota, the mean speed on interstate highways is 68.3 mph. Denote the mean to be , and assume that the distribution is normal and .
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Find the probability that a randomly chosen vehicle is traveling faster than the 65 mph speed limit.
What percentage of vehicles travel slower than 60 mph?
What proportion of vehicles travel at speeds between 65 and 68.3 mph?
The National Motorists Association asserts that speeding tickets should be issued only for drivers whose speeds exceed the 85th percentile. If the police in South Dakota followed this rule, then at what speed would they start handing out speeding tickets?
Suppose that someone from South Dakota never drives faster than 55 mph on the interstate. Is this unusual? On what do you base your answer?