Elementary Statistics (12th Edition)

Published by Pearson
ISBN 10: 0321836960
ISBN 13: 978-0-32183-696-0

Chapter 5 - Discrete Probability Distributions - 5-5 Poisson Probability Distributions - Basic Skills and Concepts - Page 233: 8

Answer

0.06, not unlikely.

Work Step by Step

By using the formula: $P(12)=\frac{\mu^k\cdot e^{-\mu}}{x!}=\frac{8.5^{12}\cdot e^{-8.5}}{12!}=0.06.$ If a value is unusual, then it is more than two standard deviations far from the mean. $Minimum \ usual \ value=mean-2\cdot(standard \ deviation)=8.5-2\cdot\sqrt{8.5}=2.67$ $Maximum \ usual \ value=mean+2\cdot(standard \ deviation)=8.5+2\cdot\sqrt{8.5}=14.33$. 12 is between the two bounds therefore it is not unlikely.
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