Question

Studies by the Federal Highway Administration suggest that speed limits on many thoroughfares are set arbi-trarily, and are often artificially low. According to traffic engineers, the ideal speed limit should be the 85thpercentile speed: this means that speed at or below which 85 percent of the traffic moves. Assuming speeds arenormally distributed, find the 85thpercentile speed for roads with the following conditions.

•The mean speed is 52 mph with a standard deviation of 8 mph,

•The mean speed is 30 mph with a standard deviation of 5 mph.

Answer 1

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Ans. For mean speed 52 mph and standard deviation 8mph

85 the percentile speed is = 60.32 mph

Ans. For mean speed 30 mph and standard deiation 5mph

85th percentile speed is 35.2 mph