Lesson: Measures of Central Tendency

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Lesson Objective

We will be able to describe a set of data using mean, median, mode, and range.

Lesson Plan

Do Now: (5 minutes)

1) A sweater that usually sells for $35 is on sale for 30% off. If the sales tax rate is 5.5%, what is the total cost of the sweater on sale?
 
2) Which is greater: |-5| or |2|
 
3) 15 is 30% of what number?

Direct Instruction: (20 minutes)

Today we are going to work with measures of central tendency. Why do you think it’s important for us to understand what measures of central tendency are? Why do you think we have different measures of central tendency?
 
Your final grade for the advisory is an average of all of your grades. The average, also called the mean, is used because it gives the best picture of your performance over the course of the advisory. The mean evens things out. It wouldn’t be fair if your entire grade was based on just one day’s work. Using an average gives the best picture of your overall performance.
 
Mean
1) Add all numbers in the data set
2) Divide by the total by the number of items in the data set.
 
Ex. Adam earned $14, $10, $12, $15, and $ 13 by doing chores around the house. What is the mean amount Adam earned doing these chores?
 
Ex. On a math quiz, 3 students scored a 90%, 2 students had an 85%, and 5 students had an 95%. What is the mean of the scores on the math quiz?
 
 
Sometimes there are outliers in a data set. When this happens, it can be more useful to use a measure of central tendency other than mean. For example, if we were trying to get a picture of the money you make from a job, and one job paid you $1,000, while all of the others paid between $200 and $250, it would be an outlier.
 
Median- the number in the middle
Ex. Find the mode: 20 yds, 15 yds, 20 yds, 11 yds, 7 yds
 
 
Mode- the number that occurs the most
Ex. The number of dogs groomed each week: 65, 56, 57, 75, 76, 77, 64
 
Range- the difference between the highest and lowest number
Ex. The highest score on a test was 100% and the lowest score on a test was 56%. What is the range of the data?
 
Complete the following table as a class:
Measure of Central Tendency
 
Most Useful When…
 
 
·         Data set has no outliers
 
·         Data set has outliers
·         There are no big gaps in the middle of the data
 
·         Data set has many identical numbers
 
 
·         Describing the spread of data
 

Guided Practice: (10 minutes)
central tendency guided practice

Assessment: (10 minutes)
measures of central tendency work-out

Lesson Resources

measures of central tendency guided practice   Classwork
1,137
measures of central tendency work out   Assessment
883
G8 2 notes   Notes
592

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