The document discusses different measures of central tendency, including the mean and median. It introduces the concept of using sigma notation to simplify writing out long sums, such as when calculating the mean of a data set. It provides an example of entree prices from a restaurant and encourages writing out the formula to calculate the mean using sigma notation.

1. Measures of Center By looking at the following stemplot of the costs of entrées at my favorite restaurant, can you make an estimate of the average cost? (Just by looking, no calculations!) There are actually two ways to find an “average” mathematically: the mean and the median . How can we find the median cost of an entrée? The mean? The mean and the median are known as measures of center . Why do you think that is? 1 2 3 4 9 4 5 8 7 9 1

2. Sigma Notation To simplify our notation when we are writing long sums (such as finding the mean), mathematicians have invented Sigma Notation . If we present our entrée costs in a list: Where Then the formula for the mean can be written using sigma notation like this:

3. Let’s explore sigma notation a bit:

4. Now, if we go back to our list of entrée prices: We said that the mean could be found using How?

5. Try writing a formula using sigma notation for the following sets of numbers: