Explanation:
Data values:
- 50- 1
- 57- 2
- 60- 4
- 65- 3
- 72- 3
- 75- 12
- 77- 10
- 81- 6
- 83- 6
- 88- 9
- 90- 12
- 92- 12
- 95- 2
- 99- 4
- 100- 5
Question 1: What is the mean? The standard deviation?
The mean = the average = all of the data values added together and then divided by the number of data values.
The standard deviation= the average of the squared differences from the mean.
Mean calculations: All of the data values added together= 50+57+57+60+60+60+60+65+65+65+72+72+72+75+75+75+75+75+75+75+75+75+75+75+75+77+77+77+77+77+77+77+77+77+77+81+81+81+81+81+81+83+83+83+83+83+83+88+88+88+88+88+88+88+88+88+90+90+90+90+90+90+90+90+90+90+90+90+92+92+92+92+92+92+92+92+92+92+92+92+95+95+99+99+99+99+100+100+100+100+100=7531
Number of data values: 91
7531/91= 82.75824175 = 82.8
The mean is 82.8.
Standard deviation:
11.34347 (sample)
11.28097 (population)
Let's go with population because this appears to be all of the grades.
11.28097 is the standard deviation (population).
Part 2: Explain how to find the standard deviation.
1. Find the mean.
2. For each data value (number), subtract the mean and square the difference (result)
3. Find the mean of those differences.
Part 3: The data values are very spread out.
Part 4: The μ sign represents population mean. The σ sign represents population standard deviation.
1. Population mean + population standard deviation=
(82.75824175) + (11.28097) = 94.03921175
1. Population mean - population standard deviation=
(82.75824175) - (11.28097) = 71.47727175
2. Population mean + 2(population standard deviation)=
(82.75824175) + 2(11.28097) = 105.32018175
2. Population mean - 2(population standard deviation)=
(82.75824175) - 2(11.28097) = 60.19630175
3. Population mean + 3(population standard deviation)=
(82.75824175)+3(11.28097) = 116.60115175
3. Population mean - 3(population standard deviation)=
(82.75824175)-3(11.28097) = 48.91533175
Page 2: Find the percentage of test scores within each range listed in question 4.
1. Range of one standard deviation = 71.47727175 - 94.03921175
How many answers are in this range? (greater than 71 but less than 95)
- 72- 3
- 75- 12
- 77- 10
- 81- 6
- 83- 6
- 88- 9
- 90- 12
- 92- 12
3+12+10+6+6+9+12+12= 70.
Total test scores = 91
70/91 = 76.92307692%
2. Range of two standard deviations= 60.19630175-105.32018175
How many answers are in this range? (greater than 60, but less than 106)
- 65- 3
- 72- 3
- 75- 12
- 77- 10
- 81- 6
- 83- 6
- 88- 9
- 90- 12
- 92- 12
- 95- 2
- 99- 4
- 100- 5
3+3+12+10+6+6+9+12+12+2+4+5 = 84
84/91 = 92.3076923%
3. Range of three standard deviations= 48.91533175- 116.60115175
How many answers are in this range? (greater than 48 but less than 117)
The lowest test score was a 50. The highest was a 100.
100%
1. Range of one standard deviation = 76.92307692%
2. Range of two standard deviations= 92.3076923%
3. Range of three standard deviations= 100%
Question 5: Does the data indicate a normal distribution? No
Question 6: Why not?
For normal distribution, 68.2 % is within one standard deviation.
95.4% is within two and 99.7 is within 3.
This data doesn't demonstrate that pattern.