Suppose X is a normal random

variable with mean μ = 70 and standard deviation σ = 5. Find b such that P(70 ≤ X ≤ b) = 0.3.

 HINT [See Example 3.] (Round your answer to one decimal place.) 

b =______

IQ scores (as measured by the Stanford-Binet intelligence test) are normally distributed with a mean of 90 and a standard deviation of 17. Find the approximate number of people in the United States (assuming a total population of 280,000,000) with an IQ higher than 130. (Round your answer to the nearest hundred thousand.)

 _____people

This exercise uses the normal probability density function and requires the use of either technology or a table of values of the standard normal distribution. 

The cash operating expenses of the regional phone companies during the first half of 1994 were distributed about a mean of $29.82 per access line per month, with a standard deviation of $2.55. Company A’s operating expenses were $28.00 per access line per month. Assuming a normal distribution of operating expenses, estimate the percentage of regional phone companies whose operating expenses were closer to the mean than the operating expenses of Company A were to the mean. (Round your answer to two decimal places.) 

_____ %

This exercise uses the normal probability density function and requires the use of either technology or a table of values of the standard normal distribution. 

The cash operating expenses of the regional phone companies during the first half of 1994 were distributed about a mean of $29.66 per access line per month, with a standard deviation of $2.25. Company N’s operating expenses were $34.53 per access line per month in the first half of 1994. Estimate the percentage of regional phone companies whose operating expenses were higher than those of Company N. (Round your answer to two decimal places.) 

_____ %

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