A suitable probability calculator will tell you that probabilty is about 25.9%.
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The normalcdf function on this calculator gives an area between a lower and upper limit. If the upper limit is more than about 8 standard deviations above the mean, the 10th decimal place is unaffected. Since the standard deviation here is about 5, we need to have an upper limit that is about 40 above the mean of about 30. We have chosen 80 as a nice round number and to give a little more margin.
The answer is false. The radius is half the diameter, not 2 times it.
The answer is 623/800 and that is in simplest form.
Cost per mile P- total cost (C) divided by total miles (M).
P= C/M