# Standard Deviation and Frequency Distributions

Pages: 5 (968 words) Published: November 19, 2012
TUI
Frequency Distributions
Module 3/Case
10/148/2012
Professor Kuleshov

Frequency Distributions
This assignment is based on Frequency Distributions and will include the following information: 1.The ability to describe the information provided by the Standard Deviation. 2.The ability to use the Standard Deviation to calculate the percentage of occurrence of a variable either above or below a particular value. 3.The ability to describe a normal distribution as evidenced by a bell shaped curve as well as the ability to prepare a distribution chart from a set of data (module 3 Case).

Part 1
(1) To get the best deal on a CD player, Tom called eight appliance stores and asked the cost of a specific model. The prices he was quoted are listed below: \$ 298 \$ 125 \$ 511 \$ 157 \$ 231 \$ 230 \$ 304 \$ 372 Find the Standard deviation \$ 298 + \$ 125+ \$ 511+ \$ 157+ \$ 231+ \$ 230+ \$ 304+ \$ 372= 2228/8 = 278.5(subtract from #s) 19,-153, 232, -121, -47, -48, 25, 93 (square numbers)

380, 2356, 54056, 14762, 2256, 2352, 650, 8742 = 106(added)
(Divide by 7) 15251 (take square root) Standard Deviation = approximately 123. (2) When investigating times required for drive-through service, the following results (in seconds) were obtained. Find the range, variance, and standard deviation for each of the two samples, and then compare the two sets of results. Wendy's 120 123 153 128 124 118 154 110

MacDonald's 115 126 147 156 118 110 145 137

(2) Set 1:
Range : maximum - minimum = 154-110= 44

Number of cases 8
To find the mean, add all of the observations and divide by 8 Mean 125
Squared deviations
(120-125)^2 = (-5)^2 = 25
(123-125)^2 = (-2)^2 = 4
(153-125)^2 = (28)^2 = 784
(128-125)^2 = (3)^2 = 9
(124-125)^2= (-1)^2= 1
(118-125)^2 = (-7)^2 = 49
(154-125)^2 = (29)^2 = 841
(110-125)^2 = (-15)^2 = 225
Add the squared deviations and divide by 8
Variance = 1938/7
Variance = 276
Standard deviation = sort(variance) = 16

Set 2:
Range : 156-110 =46

Number of cases 8
To find the mean, add all of the observations and divide by 8 Mean 131
Squared deviations
(115-131)^2 = (-16)^2 = 280
(126-131)^2 = (-5.75)^2 = 33
(147-131)^2 = (15)^2 = 232
(156-131)^2 = (24)^2 = 588
(118-131)^2 = (-13)^2 = 189
(110-131)^2 = (-21) ^2 = 473
(145-131) ^2 = (13) ^2 = 175
(137-131) ^2 = (5) ^2 = 27
This is divide by 7 because this is a sample data n-1=7
Add the squared deviations and divide by 7
Variance = 1999/7
Variance = 285
Standard deviation = sort (variance) = 16

The standard deviation for restaurant B is slightly smaller than that of restaurant A. The range for restaurant A is slightly less the range of B. This shows there is a little more variation in restaurant A with respect to times required for drive through service than in required for drive through service than in B.

(3) A company had 80 employees whose salaries are summarized in the frequency distribution below. Find the standard deviation. Find the standard deviation of the data summarized in the given frequency distribution. Salary Number of Employees

5,001 -10,000 14
10,001 - 15,000 13
15,001 - 20,000 18
20,001 - 25,000 18
25,001 - 30,000 17
The chart gives frequency and salary, traditional formulas cannot be used due to we do not know the actually salary of each employee. In order to do these assumptions need to be done with using middle point. Example (10000-5001) /2 then added to 5001= 7500

5,001- 10,000 =7500
10,001-15000=12500
15001-20000=17500
2001-2500=22500
25001-30,000=27500
Total number of employees = 80
14, 13, 18, 18, 17= 80
Compute the Mean
14 * 7500 = 105000
13* 12500 = 162500
18* 17500 = 315000
18* 22500= 405000
17 * 27500 = 467500
467500
80
Add up all frequency Mark values Total= 1455000
1455000
80
1455000 / 80 = 18187.5 = 18188
Now standard deviation
Total employees 80
Total 1455000
Means=...