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# Digital textbook std ix

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### Digital textbook std ix

1. 1. STATISTICS ARITHMETIC MEAN Learning Objectives :  Understand the mean of a set of numerical data.  Compute the mean of a given set of data.  Understand the mean of a set of data as it applies to real world situations. Introduction You are getting ready to begin a unit in Math that deals with measurement. Your teacher wants you to use benchmarks to measure the length of some objects in your classroom. A benchmark is simply a standard by which something can be measured. One of the benchmarks that you can all use is your hand span. Every student in the class must spread their hand out as far as possible and places it on top of a ruler or measuring tape. The distance from the tip of your thumb to the tip of your pinky is your hand span. Your teacher will record all of the measurements. The following results were recorded by a class of thirty-five students: Hand span (inches) Frequency 6.5 1 7.25 3 7.5 5 7.75 7 8.25 10 8.5 11 Later in this lesson, we will compute the mean or average hand span for the class. The term “central tendency” refers to the middle value or a typical value of the set of data which is most commonly measured by using the three m’s – mean, median and mode. In this lesson we will explore the mean and then move onto the median and the mode in the following lessons.
2. 2. The mean, often called the “average” of a numerical set of data, is simply the sum of the data numbers divided by the number of numbers. This value is referred to as an arithmetic mean. The mean is the balance point of a distribution. Example 1: In a recent hockey tournament, the number of goals scored by your school team during the eight games of the tournament were 4,5,7,2,1,3,6,4. What is the mean of the goals scored by your team? Solution: You are really trying to find out how many goals the team scored each game.  The first step is to add the number of goals scored during the tournament. 4 5 7 2 1 3 6 4 (The sum of the goals is 32)  The second step is to divide the sum by the number of games played. 32/8 = 4 From the calculations, you can say that the team scored a mean of 4 goals per game. Example 2: The following numbers represent the number of days that 12 students bought lunch in the school cafeteria over the past two months. What is the mean number of times that each student bought lunch at the cafeteria during the past two months? 22, 23, 23, 23, 24, 24, 25, 25, 26, 26, 29, 30 Solution: The mean is (22+23+23+23+24+24+25+25+26+26+29+30)/12 The mean is 300/12 The mean is 25 Each student bought lunch an average of 25 times over the past two months.
3. 3. If we let x represent the data numbers and n represent the number of numbers, we can write a formula that can be used to calculate the mean x of the data. The symbol Σmeans “the sum of”and can be used when we write a formula for calculating the mean. Mean = [Σ(x1+x2+…+xn)]/n Now, the mean can be calculated by multiplying each value by its frequency, adding these results, and then dividing by the total number of values (the sum of the frequencies). The formula that was written before can now be written to accommodate the values that appeared more than once. Mean =[ Σ(x1f1+x2f2+…+xnfn)/(f1+f2+…+fn)] Now we will return to the problem that was posed at the beginning of the lesson – the one that dealt with hand spans. Hand span (inches) Frequency 6.5 1 7.25 3 7.5 5 7.75 7 8.25 10 8.5 11 Solution: Mean = =[ Σ(x1f1+x2f2+…+xnfn)/(f1+f2+…+fn)] = [6.5(1)+7.25(3)+7.5(5)+7.75(7)+8.25(10)+8.5(11)]/(1+3+5+7+10+11) = 296/37 = 8 The mean hand span for 37 students is therefore 8 inches. Lesson Summary You have learned the significance of the mean as it applies to a set of numerical data. You have also learned how to calculate the mean when the data is presented as a list of numbers as well as when it is represented in a frequency table. To facilitate the process of calculating the mean, you have also learned to apply the formulas necessary to do the calculations.
4. 4. Points to Consider  Is the mean only important as a measure of central tendency?  If data is represented in another way, is it possible to either calculate or estimate the mean from this other representation? Review Questions: Show all work necessary to answer each question. Be sure to include any formulas that are needed. 1. Find the mean of each of the following sets of numbers: a) 3, 5, 5, 7, 4, 8, 6, 2, 5, 9 (5.4) b) 8, 3, 2, 0, 4, 3, 4, 6, 7, 9, 5 (4.64) c) 3, 8, 4, 1, 8, 7, 5, 6, 3, 7, 2, 9 (5.25) d) 18, 28, 27, 27, 23, 22, 25, 21, 1 (21.33) 2. The frequency table below shows the number of Tails when four coins are tossed 64 times. What is the mean? Number of tails Frequency 4 3 3 23 2 16 1 17 0 5 (2.03)