Business Stats fraction of calls
Statistics

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A study of longdistance phone calls made from General Electric Corporate Headquarters in Fairfield, Connecticut, revealed the length of the calls, in minutes, follows the normal probability distribution. The mean length of time per call was 3.70 minutes and the standard deviation was 0.60 minutes. What fraction of the calls last between 3.00 and 5.50 minutes? (Round zscore computation to 2 decimal places and your final answer to 4 decimal places.) 
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To make a probability calculation involving a normal distribution, it is helpful to translate the given distribution into the standard normal distribution so that the standard normal table can be used. The translatION is done by calculating a zscore for each of 3.00 and 5.00, then consulting a table to see what proportion of the area under the standard normal curve is between z(3) and z(5). The zscore formula is shown below.
Please let me know if you need any clarification. I'm always happy to answer your questions.Then z(3) = (3  3.70) / 0.60 = 1.17 and z(5) = (5  3.70) / 0.60 = 2.17, so the fraction of calls lasting between 3 and 5 minutes is the proportion of the area under the STANDARD normal curve between
z = 1.17 and z = 2.17. That proportion can be looked up in a table or calculated online to be: 0.864 OR ABOUT 864 OUT OF 1000.
That was not correct :(
I just entered that and it was incorrect.
Can you try this one
Cities with a population of more than 250,000 the mean oneway commute time to work is 24.3 minutes. The longest oneway travel time is in New York where the mean time is 38.8 minutes. Assume the distribution of travel times in New York follows the normal probability distribution and the standard deviation is 7.7 minutes.
ROUND ALL ANSWERS TO TWO DECIMAL PLACES
What % of commutes are less than 27 minutes
What % are between 27 & 35 minutes?
What % are between 27 and 43 minutes?Secure Information
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