the mean is 7 hours and the standard deviation is 1 hour
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Assuming a normal distribution we can calculate a Z score=(X-m)/s, where X=9.4hr, m=pop mean=7hr, s=pop standard deviation=1hr.

Z=(9.4-7)/1=2.4.

p(≤2.4)=99.18% (from tables).

So p(≥2.4)=100-99.18=0.82%.

by Top Rated User (816k points)

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