Question

6.1 question 16 please make answer clear

Electricity bills: According to a government energy agency, the mean monthly household electricity bill in the United States in 2011 was $109.99. Assume the amounts are normally distributed with standard deviation $17.00. Use the TI-84 Plus calculator to answer the following.

(a) What proportion of bills are greater than $120?

(b) What proportion of bills are between $80 and $135?

(c) What is the probability that a randomly selected household had a monthly bill less than $105? Round the answers to at least four decimal places.

Answer 1

Let "X" be the monthly electricity bill.

Note: P(Z>a)=1-P(Z<a)

Refer Standard normal table/Z-table to find the probability or use excel formula "=NORM.S.DIST(0.5888, TRUE)" to find the probability.

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Note: P(a<Z<b)=P(Z<b)-P(Z<a)

Refer Standard normal table/Z-table to find the probability or use excel formula "=NORM.S.DIST(1.4712, TRUE)" & "=NORM.S.DIST(-1.7641, TRUE)" to find the probability.

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Refer Standard normal table/Z-table to find the probability or use excel formula "=NORM.S.DIST(-0.2935, TRUE)" to find the probability.