Question

Trucks in a delivery fleet travel a mean of 120 miles per day with a standard deviation of 23 miles per day. The mileage per day is distributed normally. Find the probability that a truck drives less than 159 miles in a day. Round your answer to four decimal places.

Answer 1

the probability that a truck drives less than 159 miles in a day = 0.9374

Explanation:

Given;

mean of the truck's speed, (m) = 120 miles per day

standard deviation, d = 23 miles per day

If the mileage per day is normally distributed, we use the following conceptual method to determine the probability of less than 159 miles per day;

1 standard deviation above the mean = m + d, = 120 + 23 = 143

2 standard deviation above the mean = m + 2d, = 120 + 46 = 166

159 is below 2 standard deviation above the mean but greater than 1 standard deviation above the mean.

For normal districution, 1 standard deviation above the mean = 84 percentile

Also, 2 standard deviation above the mean = 98 percentile

143 --------> 84%

159 ---------> x

166 --------- 98%

`(159-143)/(166-143) = (x-84)/(98-84) \\\\(16)/(23) = (x-84)/(14) \\\\23(x-84) = 224\\\\x-84 = 9.7391\\\\x = 93.7391\ \%`

Therefore, the probability that a truck drives less than 159 miles in a day = 0.9374