Sample question (interpreting area of normal curve based on standard deviation) --

It is known that the mean score of Americans watching TV is 15 hours/week with the standard deviation, 4. It is also know that the distribution of hours of watching TV is normal (similar to the Gaussian curve).

Q. If this holds the truth, how many (the percentage) people are watching TV less than 7 hours?

A. 2.5 %

Q. If this holds the truth, how many (the percentage) people are watching TV more than 19 hours?

A. 50 - 34 = 16 %

Q. If the above holds the truth, how many (the percentage) people are watching TV in between 11 hours to 19 hours?

A. 68%

Q. If the above holds the truth, how many (the percentage) people are watching TV either less than 11 hours or more than 23 hours?

A. 50  34 = 16 % (less than 11 hours/week) AND 50 - 47.5 = 2.5 %: Therefore, 16 + 2.5 = 18.5 %

-- hyo kim (hkimscil@rci.rutgers.edu), October 25, 1999

Answers

Here is the picture of the area of normal curve:

The mean = 15; Standard Deviation = 4;

You need to figure out each part and/or the combination of parts.

Thanks.

-- hyo kim (hkimscil@rci.rutgers.edu), October 25, 1999.