Question

The times of the runners in a marathon are normally distributed, with a mean of 3 hours and 50 minutes and a standard deviation of 30 minutes. What is the probability that a randomly selected runner has a time less than or equal to 3 hours and 20 minutes? Use the portion of the standard normal table below to help answer the question. z Probability 0.00 0.5000 0.50 0.6915 1.00 0.8413 2.00 0.9772 3.00 0.9987

Answer 1

Answer: 0.16

Step-by-step explanation:

Given that the run times provided are normally distributed ;

Mean(x) of distribution = 3 hours 50 minutes

Standard deviation(s) = 30 minutes

The probability that a randomly selected runner has a time less than or equal to 3 hours 20 minutes

3 hours 20 minutes = (3 hrs 50 mins - 30 mins):

This is equivalent to :

[mean(x) - 1 standard deviation]

z 1 standard deviation within the mean = 0.84

z, 1 standard deviation outside the mean equals:

P(1 - z value , 1standard deviation within the mean)

1 - 0.8413 = 0.1587

= 0.16