Question

Internet providers: In a survey of 961 homeowners with high-speed Internet, the average monthly cost of a high-speed Internet plan was $74.54 with standard deviation $11.08. Assume the plan costs to be approximately bell-shaped. Estimate the number of plans that cost between $52.38 and $96.7. Round to the nearest whole number. The number of plans that cost between $52.38 and $96.7 is .

Answer 1

The number of plans that cost between $52.38 and $96.7 is 913.

Explanation:

The Empirical Rule states that, for a normally distributed random variable:

Approximately 68% of the measures are within 1 standard deviation of the mean.

Approximately 95% of the measures are within 2 standard deviations of the mean.

Approximately 99.7% of the measures are within 3 standard deviations of the mean.

In this problem, we have that:

Mean of $74.54, standard deviation of $11.08

Percentage of plans that cost between $52.38 and $96.7.

52.38 = 74.54 - 2*11.08

96.7 = 74.54 + 2*11.08

Within 2 standard deviations of the mean, so by the Empirical Rule, 95%.

The number of plans that cost between $52.38 and $96.7 is .

95% of 961. So

0.95*961 = 913

The number of plans that cost between $52.38 and $96.7 is 913.