Elementary Statistics (12th Edition)

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

Chapter 5 - Discrete Probability Distributions - 5-3 Binomial Probability Distributions - Basic Skills and Concepts - Page 220: 36


0.1247, it is not an unusually low number.

Work Step by Step

$P(X=20)={30\choose 20} \cdot (0.72)^{20}\cdot (0.28)^{10}=0.1247.$ $P(X\leq20)\geq P(X=20)=0.1247$, therefore it's probability will be quite big (bigger than 0.05), therefore it is not an unusually low number.
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