SOLUTION: According to the records of an electric company serving the Boston area, the mean electricityconsumption for all households during winter is 1650 kilowatt-hours per month. Assume

Question 1103585: According to the records of an electric company serving the Boston area, the mean electricityconsumption for all households during winter is 1650 kilowatt-hours per month. Assume that themonthly electricity consumptions during winter by all households in this area have a normal dis-tribution with a mean of 1650 kilowatt-hours and a standard deviation of 320 kilowatt-hours. Thecompany sent a notice to Bill Johnson informing him that about 90% of the households use lesselectricity per month than he does. What is Bill Johnson's monthly electricity consumption?
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
Normal distribution with mean is 1650 and sd is 320.
Basically, 90th percentile of z is +1.282
z=(x-mean)/sd
1.282=(x-1650)/320
410.24=x-1650
x=2060 kwh.

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