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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.
