Question

An engineering crew ran several tests on a new automobile engine they were designing. The mean fuel consumption was 52.4 miles per gallon and the standard deviation was 1.8 mpg. Which mpg test would be considered an "unusual" value? O54.8 mpg O56.5 mpg 049.1 mpg O51.3 mpg

Answer 1

Any value which is more than 2 standard deviations away from the mean is considered to be "unusual."  

2 standard deviations above the mean 52.4 mp would be 52.4+2(1.8), or 56; 2 std devs below the mean would be 52.4 - 2(1.8), or 48.8.  Thus, any value larger than 56 or any value smaller than 48.8 would be "unusual."

54.8, 49.1 and 51.3 are not unusual; 56.5 is unusual, because it's greaster than 56.