6.6 (Please use Normal Approximation to Binomial Methods) #20 Cell Phones and Br
ID: 3360465 • Letter: 6
Question
6.6 (Please use Normal Approximation to Binomial Methods) #20 Cell Phones and Brain Cancer In a study of 420095 cell phone users in Denmark, it was found that 135 developed cancer of the brain or nervous system. For those not using cell phones, there is a 0.000340 probability of a person developing cancer of the brain or nervous system. We therefore expect about 143 cases of such cancers in a group of 420095 randomly selected people. a. Find the probability of 135 or fewer cases of such cancers in a group of 420095 people. b. What do these results suggested about media reports that suggest cell phones cause cancer of the brain or nervous system?Explanation / Answer
Solution:
(a) Given n = 420,095
p = 0.000340
mean µ = np = 420,095 * 0.000340 = 142.83
Standard deviation s = sqrt(np(1-p))=sqrt(420.095×0.000340×0.99966)
= sqrt(142.7837) = 11.95
(b) Given µ-2s = 142.83-2(11.95) = 118.93?119
µ+2s = 142.83+2(11.95) = 166.73 167
Since the value 135 lies between the minimum usual value 119 and the maximum usual value 167, it is not unusual.
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