Question

Electricity bills: According to a government energy agency, the mean monthly household electricity bill in the United States in was . Assume the amounts are normally distributed with standard deviation . Use the TI-84 Plus calculator to answer the following. (a) Find the th percentile of the bill amounts. (b) Find the rd percentile of the bill amounts. (c) Find the median of the bill amounts. Round the answers to at least two decimal places

Answer 1

The 9th percentile of the bill amounts is 81.0634.

How to calculate the percentile?

Population mean, µ = 110.56

Population standard deviation, σ = 22

a) p = 0.09

Z score at p = 0.09 using excel = NORM.S.INV(0.09) = -1.3408

Value of X = µ + z*σ = 110.56 + (-1.3408)*22 = 81.0634

9th percentile = 81.0634

b) p = 0.66

Z score at p = 0.66 using excel = NORM.S.INV(0.66) = 0.4125

Value of X = µ + z*σ = 110.56 + (0.4125)*22 = 119.6342

66th percentile = 119.6342

c) Median = 0.50

Z score at p = 0.5 using excel = NORM.S.INV(0.5) = 0

Value of X = µ + z*σ = 110.56 + (0)*22 = 110.56

Median = 110.56

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