1. A radar unit is used to measure the speed of automobiles on the expressway during the rush-hour traffic. The speed of individual automobiles are normally distributed with a mean of 62 mph. (a) If the standard deviation is about 4.95 mph, what is the proportion of the cars that are traveling in 70 mph or less? (b) Find the 25th percentile, using the standard deviation of Part (a). (c) If 3% of the automobiles travel faster than 72 mph, what is the standard deviation? (d) Find the proportion of the cars that are traveling faster than 55 mph, using the standard deviation found in Part (c). (e) Find the 95th percentile, using the standard deviation of Part (c).

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1. A radar unit is used to measure the speed of automobiles on the expressway during the
rush-hour traffic. The speed of individual automobiles are normally distributed with a mean
of 62 mph.
(a) If the standard deviation is about 4.95 mph, what is the proportion of the cars that are
traveling in 70 mph or less?
(b) Find the 25th percentile, using the standard deviation of Part (a).
(c) If 3% of the automobiles travel faster than 72 mph, what is the standard deviation?
(d) Find the proportion of the cars that are traveling faster than 55 mph, using the standard
deviation found in Part (c).
(e) Find the 95th percentile, using the standard deviation of Part (c).
2. According to a September 2008 poll and report done by Pew/Internet, 62% of employed
adults use the Internet or e-mail on their jobs.
(a) Use the normal approximation to estimate the probability that more than 170 out of
250 employed adults use the Internet or e-mail on their jobs.
(b) Use the normal approximation to estimate the probability that more than 2/3 of 250
employed adults use the Internet or e-mail on their jobs.
Transcribed Image Text:Name: 1. A radar unit is used to measure the speed of automobiles on the expressway during the rush-hour traffic. The speed of individual automobiles are normally distributed with a mean of 62 mph. (a) If the standard deviation is about 4.95 mph, what is the proportion of the cars that are traveling in 70 mph or less? (b) Find the 25th percentile, using the standard deviation of Part (a). (c) If 3% of the automobiles travel faster than 72 mph, what is the standard deviation? (d) Find the proportion of the cars that are traveling faster than 55 mph, using the standard deviation found in Part (c). (e) Find the 95th percentile, using the standard deviation of Part (c). 2. According to a September 2008 poll and report done by Pew/Internet, 62% of employed adults use the Internet or e-mail on their jobs. (a) Use the normal approximation to estimate the probability that more than 170 out of 250 employed adults use the Internet or e-mail on their jobs. (b) Use the normal approximation to estimate the probability that more than 2/3 of 250 employed adults use the Internet or e-mail on their jobs.
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