The Basic Practice of Statistics 7th Edition

Published by W. H. Freeman
ISBN 10: 146414253X
ISBN 13: 978-1-46414-253-6

Chapter 3 - The Normal Distributions - Chapter 3 Exercises - Page 95: 3.27

Answer

2.5%

Work Step by Step

Under the 68-95-99.7 rule, 95% of the population is within two standard deviations of the mean. This means that 2.5% of the population is more than two (negative) deviations from the mean. $(70-100)/15 = z$ $-30/15 = -2 = z$
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