Question

There is an unusual number of accidents reported along a certain stretch of highway, where the speed limit is 6060 miles per hour.



The township police department seeks to determine if excessive speeding is a problem along that stretch of highway and records the speed of 3030 cars (selected at random) that are using that highway.

The table below shows the 3030 speeds.



576468, 58,64,68,59,64,69, 60,65,69, 61,65,70,62,66,70,63,66,70,63,66,71,63,67,72,63,67,75







Using this data, estimate the mean speed of all cars and identify the range of speeds within 22 standard deviations of the mean.



Mean =
miles per hour.

Standard deviation ≈
miles per hour.



Lower range (+2 S.D.) =


Upper range (+2 S.D.) =

Answer 1

Mean = 65.50 miles per hour

Standard deviation ≈ 4.28 miles per hour

Lower range (mean − 2·SD) ≈ 65.50 − 2(4.28) = 56.94 mph

Upper range (mean + 2·SD) ≈ 65.50 + 2(4.28) = 74.06 mph