Question

Lisa has collected data to find that the number of pages per book on a book shelf has a normal distribution. What is the probability that a randomly selected book has fewer than 133 pages if the mean is 189 pages and the standard deviation is 28 pages? Use the empirical rule.Enter your answer as a percent rounded to two decimal places if necessary.

Answer 1

Answer:

2.5% probability that a randomly selected book has fewer than 133 pages.

Step-by-step explanation:

The Empirical Rule states that, for a normally distributed random variable:

68% of the measures are within 1 standard deviation of the mean.

95% of the measures are within 2 standard deviation of the mean.

99.7% of the measures are within 3 standard deviations of the mean.

In this problem, we have that:

Mean = 189 pages

Standard deviation = 28 pages

What is the probability that a randomly selected book has fewer than 133 pages?

133 = 189 - 2*28

So 133 is two standard deviations below the mean.

The Empirical Rule states that 95% of the measures are within 2 standard deviations of the mean. The other 5% is more than two standard deviations distant from the mean. The normal distribution is symmetric, which means that of those 5%, 2.5% are more than 2 standard deviations below the mean and 2.5% are more than 2 standard deviations above the mean.

This means that there is a 2.5% probability that a randomly selected book has fewer than 133 pages.