Difference between revisions of "AP Statistics Curriculum 2007 Normal Std"
| Line 2: | Line 2: | ||
=== Standard Normal Distrribution=== | === Standard Normal Distrribution=== | ||
| − | The standard normal distribution is a continuous distribution where the | + | The standard normal distribution is a continuous distribution where the following exact ''areas'' are bound between the Standard Normal Density function and the x-axis on the symmetric intervals around the origin: |
| − | + | * The area: -1 < z < 1 = 0.8413 - 0.1587 = 0.6826 | |
| + | * The area: -2.0 < z < 2.0 = 0.9772 - 0.0228 = 0.9544 | ||
| + | * The area: -3.0 < z < 3.0 = 0.9987 - 0.0013 = 0.9974 | ||
| + | <center>[[Image:SOCR_EBook_Dinov_RV_Normal_013108_Fig10.jpg|500px]]</center> | ||
| + | * The Standard Normal distribution is also a special case of the [[AP_Statistics_Curriculum_2007_Normal_Prob | more general normal distribution]] where the mean is set to zero and a variance to one. The Standard Normal distribution is often called the ''bell curve'' because the graph of its probability density resembles a bell. | ||
===Experiments=== | ===Experiments=== | ||
| − | + | Suppose we decide to test the state of 100 used batteries. To do that, we connet each battery to a volt-meter by randomly attaching the positive (+) and negative (-) battery terminals to the corresponding volt-meter's connections. Electrical current always flows from + to -, i.e., the current goes in the direction of the voltage drop. Depending upon which way the battery is connected to the volt-meter we can observe positive or negative voltage recordings (voltage is just a difference, which forces current to flow from higher to the lower voltage.) Denote <math>X_i</math>={measured voltage for battery i} - this is random variable 0 and assume the distribution of all <math>X_i</math> is Standard Normal, <math>X_i \sim N(0,1)</math>. Use the Normal Distribution (with mean=0 and variance=1) in the [http://socr.ucla.edu/htmls/SOCR_Distributions.html SOCR Distribution applet] to address the follwoing questions. This [[Help_pages_for_SOCR_Distributions | Disrtibutions help-page may be useful in understanding SOCR Distribution Applet]]. How many batteries, from the sample of 100, can we expect to have: | |
| − | <center>[[Image: | + | * Absolute Voltage > 1? P(X>1) = 0.1586, thus we expect 15-16 batteries to have voltage exceeding 1. |
| − | + | <center>[[Image:SOCR_EBook_Dinov_RV_Normal_013108_Fig1.jpg|500px]]</center> | |
| − | == | + | * |Absolute Voltage| > 1? P(|X|>1) = 1- 0.682689=0.3173, thus we expect 31-32 batteries to have absolute voltage exceeding 1. |
| − | + | <center>[[Image:SOCR_EBook_Dinov_RV_Normal_013108_Fig2.jpg|500px]]</center> | |
| − | + | * Voltage < -2? P(X<-2) = 0.0227, thus we expect 2-3 batteries to have voltage less than -2. | |
| − | * | + | <center>[[Image:SOCR_EBook_Dinov_RV_Normal_013108_Fig3.jpg|500px]]</center> |
| − | + | * Voltage <= -2? P(X<=-2) = 0.0227, thus we expect 2-3 batteries to have voltage less than or equal to -2. | |
| − | + | <center>[[Image:SOCR_EBook_Dinov_RV_Normal_013108_Fig3.jpg|500px]]</center> | |
| − | + | * -1.7537 < Voltage < 0.8465? P(-1.7537 < X < 0.8465) = 0.761622, thus we expect 76 batteries to have voltage in this range. | |
| − | + | <center>[[Image:SOCR_EBook_Dinov_RV_Normal_013108_Fig4.jpg|500px]]</center> | |
| − | * | ||
| − | |||
| − | === | ||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | * | ||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
<hr> | <hr> | ||
===References=== | ===References=== | ||
| − | |||
<hr> | <hr> | ||
Revision as of 15:05, 31 January 2008
Contents
General Advance-Placement (AP) Statistics Curriculum - Standard Normal Variables and Experiments
Standard Normal Distrribution
The standard normal distribution is a continuous distribution where the following exact areas are bound between the Standard Normal Density function and the x-axis on the symmetric intervals around the origin:
- The area: -1 < z < 1 = 0.8413 - 0.1587 = 0.6826
- The area: -2.0 < z < 2.0 = 0.9772 - 0.0228 = 0.9544
- The area: -3.0 < z < 3.0 = 0.9987 - 0.0013 = 0.9974
- The Standard Normal distribution is also a special case of the more general normal distribution where the mean is set to zero and a variance to one. The Standard Normal distribution is often called the bell curve because the graph of its probability density resembles a bell.
Experiments
Suppose we decide to test the state of 100 used batteries. To do that, we connet each battery to a volt-meter by randomly attaching the positive (+) and negative (-) battery terminals to the corresponding volt-meter's connections. Electrical current always flows from + to -, i.e., the current goes in the direction of the voltage drop. Depending upon which way the battery is connected to the volt-meter we can observe positive or negative voltage recordings (voltage is just a difference, which forces current to flow from higher to the lower voltage.) Denote \(X_i\)={measured voltage for battery i} - this is random variable 0 and assume the distribution of all \(X_i\) is Standard Normal, \(X_i \sim N(0,1)\). Use the Normal Distribution (with mean=0 and variance=1) in the SOCR Distribution applet to address the follwoing questions. This Disrtibutions help-page may be useful in understanding SOCR Distribution Applet. How many batteries, from the sample of 100, can we expect to have:
- Absolute Voltage > 1? P(X>1) = 0.1586, thus we expect 15-16 batteries to have voltage exceeding 1.
- |Absolute Voltage| > 1? P(|X|>1) = 1- 0.682689=0.3173, thus we expect 31-32 batteries to have absolute voltage exceeding 1.
- Voltage < -2? P(X<-2) = 0.0227, thus we expect 2-3 batteries to have voltage less than -2.
- Voltage <= -2? P(X<=-2) = 0.0227, thus we expect 2-3 batteries to have voltage less than or equal to -2.
- -1.7537 < Voltage < 0.8465? P(-1.7537 < X < 0.8465) = 0.761622, thus we expect 76 batteries to have voltage in this range.
References
- SOCR Home page: http://www.socr.ucla.edu
Translate this page:
