James Reese and Cheuk Wong

Mean (Average)  The mean, or average is the sum of the data divided by the amount of data in it.  It is used to show what is normal.  Pro: It’s a way to show what is normal.  Con: It is greatly affected by outliers.  Another Con: It sometimes results in a nonterminating, nonrepeating decimal.

Median  The median is the piece of data in the middle of the data set if there is an odd amount of data, or the number between the middle two numbers if there is an even amount.  It is used to show what is in the middle and is often more accurate than the mean, as it isn’t affected by outliers nearly as much.  Pro: It shows what is in the middle.  Con: It sometimes isn’t part of the data set.

Mode  The mode is the part of the data with the most entries, such as if in a data table, if 5 came in 3 times, 2 came in once, and 4 came in 5 times, 4 would be the mode.  It would be used to show the most popular choice in a poll.  Pro: It shows what is the most popular.  Con: It doesn’t show anything else.

Necessary Data Needed  Each measure of central tendency needs a single set of data.

Example From Outside Source  In this stem and leaf plot, the mean is about , the median is 60, and the mode is 75.  This shows how many people watched TV for how many minutes a day. From the measures of central tendency, it can be concluded that most students watch about 60 to 75 minutes of TV per day.  Image from kasiesmaps.blogspot.com

Our Constructed Example  We took a poll of how many minutes people in Mrs. Ellwood’s fourth period class thought they studied for any given test.  The results were as follows: 0, 0, 0, 0, 7, 7, 10, 10, 15, 20, 30, 40, 90, and 120. Therefore, the median was 10, the mode was 0, and the average was about

Our Problem  If Mrs. Ellwood’s time spent studying of 2 hours were added to the data (the old mean was minutes and there were 14 inputs), what would the new average be? (Round to the nearest tenth)

ANSWER TO THE PROBLEM  About 31.3

How to Answer the Problem  The results form the original were(0, 0, 0, 0, 7, 7, 10, 10, 15, 20, 30, 40, 90, and 120)  Find the average: minutes  14 inputs  Mrs. Ellwood’s time: 2 hours (120 minutes) 1) 24.93* = ) /(14+1) = ) Round to 31.3