Question

The length of a phone conversation is normally distributed with a mean of 4 minutes and a standard deviation of .6 minutes. What is the probability that a conversation lasts longer than 5 minutes? 0.04746 0.45254 0.54746 0.95254

Answer 1

Answer:

0.04746

Step-by-step explanation:

To answer this one needs to find the area under the standard normal curve to the left of 5 minutes when the mean is 4 minutes and the std. dev. is 0.6 minutes.  Either use a table of z-scores or a calculator with probability distribution functions.

In this case I will use my old Texas Instruments TI-83 calculator.  I select the normalcdf( function and type in the following arguments:  :

normalcdf(-100, 5, 4, 0.6).  The result is 0.952.  This is the area under the curve to the left of x = 5.  But we are interested in finding the probability that a conversation lasts longer than 5 minutes.  To find this, subtract 0.952 from 1.000:   0.048.  This is the area under the curve to the RIGHT of x = 5.

This 0.048 is closest to the first answer choice:  0.04746.