Answer to Question #10682 in Statistics and Probability for james

Question #10682
3. The mean time taken by all participants to run a road race was found to be 220 minutes with a standard deviation
of 20 minutes. Using the 68 – 95 – 99.7 Rule, find the percentage of runners who ran this race:

a. In less than 180 minutes
b. In more than 220 minutes
c. In between 160 and 280 minutes
d. In at least 240 minutes
e. In no more than 200 minutes
1
Expert's answer
2012-06-12T10:52:48-0400

a 2.5% (% of population less than mean-2*stdev)

b 50% (mean divides population by half, in case of normal distribution)

c 99.7% (% of population which falls between 3 stdevs around mean)

d 16% (% of population which is less than mean-stdev)

e 16% (% of population which is bigger than mean+stdev)

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