The electric company just sent you a letter with your average daily electricity

Question

The electric company just sent you a letter with your average daily electricity usage over the entire time you have lived in your house (several years). Daily usage is normally distributed with the average of 18 kilowatt-hours and a standard deviation of 4 kilowatt-hours. You are also interested in your average cost of electricity over month-long periods (30 days). What percent of months have average kilowatt usage between 16.83 kwh and 17.45 kwh? 0.72% O 71.86% O 17.18% O 17.36% 6.22% ,06% O 74.11% o 5.98%

Explanation / Answer

Solution1:

mean=18

sd=4

P(16.83<X bar<17.45)

z=x-mean/sd/sqrt(n)

z=16.83-18/4/sqrt(30)<Z<17.45-18/4/sqrt(30)

P(-1.60<z<-0.75)

=0.1718

=0.1718*100=17.18%

OPTION C

Solution2:

percentile rank for 19.91

Z=x-mean.sd

=19.19-18/4

Z =0.2975

P(Z<0.298)=0.6179

0.6179*00=61.79%

ANSWER:61.79%

option A

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