The average number of potholes per 10 miles of paved U.S. roads is 130. Assume this variable is approximately normally distributed and has a standard deviation of 5. Find the probability that a randomly selected road has between 128 and 136 potholes per mile.

54.03% probability that a randomly selected road has between 128 and 136 potholes per 10 miles.

Step-by-step explanation:

Problems of normally distributed samples are solved using the z-score formula.

In a set with mean and standard deviation , the zscore of a measure X is given by:

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.

In this problem, we have have that:

Find the probability that a randomly selected road has between 128 and 136 potholes per 10 miles.

This probability is the pvalue of Z when X = 136 subtracted by the pvalue of Z when X = 128. So

X = 136

has a pvalue of 0.8849.

X = 128

has a pvalue of 0.3446.

0.8849 - 0.3446 = 0.5403

54.03% probability that a randomly selected road has between 128 and 136 potholes per 10 miles.