# Data File 3

Data File 3
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Chapter Five

If light bulbs have lives that are normally distributed with a mean of 2500 hours and a standard deviation of 500 hours, what percentage of light bulbs have a life less than 2500 hours?

The lifetimes of light bulbs of a particular type are normally distributed with a mean of 370 hours and a standard deviation of 5 hours. What percentage of bulbs has lifetimes that lie within 1 standard deviation of the mean on either side?

The amount of Jen’s monthly phone bill is normally distributed with a mean of \$60 and a standard deviation of \$12.   Fill in the blanks:
68% of her phone bills are between \$______________ and \$______________.

The amount of Jen’s monthly phone bill is normally distributed with a mean of \$50 and a standard deviation of \$10.   Find the 25th percentile.

The diameters of bolts produced by a certain machine are normally distributed with a mean of 0.30 inches and a standard deviation of 0.01 inches.   What percentage of bolts will have a diameter greater than 0.32 inches?

The annual precipitation amounts in a certain mountain range are normally distributed with a mean of 88 inches, and a standard deviation of 10 inches. What is the likelihood that the mean annual precipitation during 25 randomly picked years will be less than 90.8 inches?

A final exam in Statistics has a mean of 73 with a standard deviation of 7.73.   Assume that a random sample of 24 students is selected and the mean test score of the sample is computed. What percentage of sample means are less than 70?

A mean score on a standardized test is 50 with a standard deviation of 10. Answer the following
What scores fall between –1 and +1 standard deviation?
What percent of all scores fall between –1 and +1 standard deviation?
What score falls at +2 standard deviations?
What percentage of scores falls between +1 and +2 standard deviations?

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Chapter Six

For the following questions, would the...