# Chapter 5 - Discrete Probability Distributions - 5-4 Parameters for Binomial Distributions - Basic Skills and Concepts - Page 227: 13

a) Mean:142.83. Standard deviation:11.95. b)It is not unusually low or high. c)These results suggest that cell phones do not increase the probability of cancer of the brain or the nervous system.

#### Work Step by Step

a) Mean=$n\cdot p=420095 \cdot 0.00034=142.83$. Standard deviation: $\sqrt{n \cdot p \cdot (1-p)}=\sqrt{420095 \cdot 0.00034 \cdot 0.99966}=11.95.$ b) If a value is unusual, then it is more than two standard deviations far from the mean. $Minimum \ usual \ value=mean-2\cdot(standard \ deviation)=142.83-2\cdot11.95=118.93.$ $Maximum \ usual \ value=mean+2\cdot(standard \ deviation)=142.83-2\cdot11.95=166.73$. 135 is between these two numbers, therefore it is not unusally low or high. c) These results suggest that cell phones do not increase the probability of cancer of the brain or the nervous system.

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