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

Expert's answer

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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