Question

Speeding on the I-5. Suppose the distribution of passenger vehicle speeds traveling on the Interstate 5 Freeway (I-5) in California is nearly normal with a mean of 72 miles/hour and a standard deviation of 5.25 miles/hour. Round all answers to four decimal places.

1. What proportion of passenger vehicles travel slower than 61 miles/hour?

2. What proportion of passenger vehicles travel between 76 and 82 miles/hour?

3. How fast do the fastest 18% of passenger vehicles travel?  

4. Suppose the speed limit on this stretch of the I-5 is 65 miles/hour. Approximately what proportion of the passenger vehicles travel above the speed limit on this stretch of the I-5?

Answer 1