Question

The 100-meter dash times in the girls track meet were normally distributed with a mean of 13 seconds and a standard deviation of 0.3 seconds. What is the probability that a runner finished between 12.4 and 14 seconds?

Answer 1

The probability is 0.97682

Explanation:

We start by finding the z-values of the runner times given.

Mathematically;

z-score = (x-mean)/SD

From the question, mean = 13 seconds and SD = 0.3 seconds

So for 12.4 seconds, we have;

z = (12.4-13)/0.3 = -0.6/0.3 = -2

For 14 seconds, we have;

z = (14-13)/0.3= 1/0.3 = 3.33

So the probability we want to calculate is;

P(-2<z<3.33)

We can find this using the standard normal distribution table

Mathematically;

P(-2<z<3.33) = P(z<3.33) - P(z < -2)

Using the standard normal distribution table, the value of this is;

P(-2<z<3.33) = 0.97682