SOLUTION: The wait time for a company before a customer can talk to a customer service representative has a mean of 140 seconds with a standard deviation of 20 seconds. Suppose the distribut

Question 929413: The wait time for a company before a customer can talk to a customer service representative has a mean of 140 seconds with a standard deviation of 20 seconds. Suppose the distribution of wait times is approximately bell-shaped and symmetric.

Which one of the following statements is correct?

A The proportion of customers whose wait time is under 120 seconds is approximately 68%
B The proportion of customers whose wait time is under 120 seconds is approximately 95%
C The proportion of customers whose wait time is more than 160 seconds is approximately 84%
D The proportion of customers whose wait time is more than 160 seconds is approximately 16%
E The proportion of customers whose wait time is more than 140 seconds is greater than the proportion whose wait time is under 140 seconds
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
mean =140sec, SD = 20 seconds,
...
P(x < 120) = p( z < -20/20) = normalcdf(-100,-1) = .1587
P(x > 120) = P(z > -1) = normalcdf(-1,100) = .8413
P(x > 160) = P(z > 20/20)= normalcdf(1,100) = .1587 0r 15.87% ***
.5000 = .5000
D.
.......
For the normal distribution: Below: z = 0, z = � 1, z= �2 , z= �3 are plotted.
Area under the standard normal curve to the left of the particular z is P(z)
Note: z = 0 (x value: the mean) 50% of the area under the curve is to the left and 50% to the right

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