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ASK THE PROFESSOR FORUM

Course Documents

Chapter 1 - Intro

Chapter 2 - Methods for Describing Sets of Data

Chapter 3 - Probability

Chapter 4 - Discrete Random Variables

Chapter 5 - Normal Random Variables

Chapter 6 - Sampling Distributions

Chapter 7 - Confidence Intervals

Chapter 8 - Tests of Hypothesis: One Sample

Chapter 9 - Confidence Intervals and Hypothesis Tests: Two Samples

Sample Exam I: Chapters 1 & 2

Sample Exam II: Chapters 3 & 4

Sample Exam III: Chapters 5 & 6

Sample Exam IV: Chapters 7 & 8

Ask the Professor Forum

HI professor, when it says what is the probability that a randomly selected males is exactly 72 inches (6ft tall)? how do you find this using the z table? this is problem 1 in the homework in 5.1 ? thanks

Posted to STATS 1 on Monday, October 28, 2013   Replies: 1


Professor Mcguckian
10/28/2013
8:32 PM EST

Hi Tufic,

If the problem says, "exactly 72 inches tall," the answer is zero since there is zero area associated with 72. 

Remember that for normally distributed random variables probability is equal to area under the curve.  To find an area under the curve, the problem must either say at least, at most, less than, more than, between, less than or equal to, greater than or equal to, ... All of those statements give you an area under the curve you can shade and find.

That is not possible if you are looking for the probability that a person is 72 inches tall.  We could find more than 72, less than 72, at least 72, at most 72, ... The answer when it is exactly 72 is just zero. 

Hope that is clear,

Professor McGuckian

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