After increased patrol,cars on a road travel at speeds averaging 54 km/h.If 10% of vehicles travel above 70 km/h,what approximate standard deviation could represent this model (assuming a Normal model is appropriate)?
A)35.94
B)12.50
C)7
D)5.4
E)-12.50

Question

Quizplus · Accepted Answer

In a normal distribution, approximately 10% of the data lies above 1.28 standard deviations from the mean. If the mean is 54 km/h and 10% of vehicles travel above 70 km/h, then 70 = 54 + 1.28*SD. Solving for SD gives approximately 12.50.

After Increased Patrol,cars on a Road Travel at Speeds Averaging