Normal Distribution of Test Scores: Percentages for Various Ranges

  • Thread starter apoechma
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The table you need to look at is the CDF (cumulative distribution function). This table is usually called the "standard normal table" It's usually found in the back of a stat book.In summary, the normal distribution is a commonly used statistical model that is often referred to as a "bell curve." It is characterized by a mean of 100 and a standard deviation of 15. The probability of getting a score within a certain range can be found by looking up the corresponding values on a standard normal table. For the given values, the percentage of the population with scores between 100 and 125 is approximately 34%, between 82 and 106 is approximately 68%, between 110 and 132 is approximately
  • #1
apoechma
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Scores on a particular test are normally distributed in the population, with a mean of 100 and a standard deviation of 15. What percentage of the population have scores ...

a) Between 100 and 125

b) Between 82 and 106

c) Between 110 and 132

d) Above 132

e) Equal to 132
HELP ME UNDERSTAND THIS PLEASE!
 
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  • #3
THe normal distribution is also know as the Gaussian distribution or a "bell curve" It is described by the equation on the wikipedia page. For your problem
mu = location of the peak probability = 100
sigma^2 = variance = standard variation = 15

You may notice the part of the equation outside the exponential. This is called a normalizing factor. This factor adusts the height of the function depending on the value of sigma so the TOTAL area under the curve is 1. THis means if you the take the test, the probaility that you have any score is 1.

The probability of getting some score between two values is simply the integral of the curve between these two scores. However, it's usless trying to actually do the integral. You need to look up the gaussian integrals in a table.
 

1. What is a continuous random variable?

A continuous random variable is a type of random variable that can take on any value within a certain range. Unlike a discrete random variable, which can only take on specific, isolated values, a continuous random variable can take on an infinite number of values within a given interval.

2. How is a continuous random variable different from a discrete random variable?

A discrete random variable can only take on specific, isolated values, while a continuous random variable can take on any value within a given interval. This means that a continuous random variable is measured on a continuous scale, while a discrete random variable is measured on a discrete scale.

3. What is the probability density function of a continuous random variable?

The probability density function (PDF) of a continuous random variable is a function that describes the probability of the variable taking on a particular value. It is represented by a curve on a graph, and the area under the curve between two points represents the probability of the variable falling within that range.

4. How is the probability of a continuous random variable calculated?

The probability of a continuous random variable falling within a certain range is calculated by finding the area under the probability density curve between the two points that define the range. This can be done using calculus by taking the integral of the probability density function.

5. What are some examples of continuous random variables?

Some examples of continuous random variables include height, weight, temperature, and time. These variables can take on an infinite number of values within a certain range and are measured on a continuous scale.

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