"It is not our conclusions that betray us. It is our major premises."  (Tom Burnam, The Dictionary of Misinformation )
Incredibly, the concept of a negative number confused mathematicians until well into the 1800's. While the Hindus and Chinese did work with negative numbers, the thought that one could have numbers less than nothing bothered even the best of mathematicians. Math texts frequently confused subtraction and the use of the minus symbol to represent opposite . Research on negative numbers will yield you some rather surprising results. The confusion is characterized by this statement from French mathematician Jean Le Rond d'Alembert (17171783).

When Herkimer was thirsty, why did he put ice cubes in this father's bed? Answer: So he could have an ice cold pop. Herky's friends: SAM PULL...he works for a polling organization. JOE KING...this guy likes to tell funny stories. 
ASSIGNMENT #29 Reading: Review chapter 4, as necessary. Exercises: Test 4A (handout in class) 
You are working with review materials for Chapter4.
Pages 229  231 contain provides a good SUMMARY ofthe important concepts introduced in Chapter 4.
Important words/phrases/thoughts introduced inthis chapter include:
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Text:
The Practice of Statistics, by Yates, Moore, McCabe. New York,W.H. Freeman and Company, 1999. (ISBN 0716733706)
Supplemental books:
The Cartoon Guide to Statistics, by Gonick and Smith. NewYork, HarperCollins Publishers, 1993. (ISBN 0062731025)
How to Lie with Statistics, by Darrell Huff. New York, W.W.Norton & Company, 1982 (ISBN 039309426X)