(STATISTICS) 3 randomly selected observations from standard norm dist

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SUMMARY

The discussion centers on calculating the probability that the sum of three randomly selected observations from a standard normal distribution is less than 2. The correct answer is established as 0.874928. Participants clarify that the sum of independent normal distributions is also normally distributed, with a mean of 0 and a standard deviation of √3. The probability can be determined using the cumulative distribution function (CDF) for the resulting normal distribution.

PREREQUISITES
  • Understanding of standard normal distribution properties
  • Knowledge of cumulative distribution functions (CDF)
  • Familiarity with the concept of summing independent random variables
  • Basic statistics, including mean and standard deviation calculations
NEXT STEPS
  • Learn how to calculate the sum of independent normal distributions
  • Study the cumulative distribution function (CDF) for normal distributions
  • Explore statistical software tools like R or Python for probability calculations
  • Investigate the Central Limit Theorem and its implications for normal distributions
USEFUL FOR

Students in statistics, data analysts, and anyone interested in probability theory and normal distribution applications.

skyturnred
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Homework Statement



3 randomly selected observations form the standard normal distribution are selected. What is the probability that their sum is less than 2?

Homework Equations





The Attempt at a Solution



I know that the answer is 0.874928, but I don't know how to get that.


In my mind, you would say that 2/3=0.67, so what is the probability that the average of the 3 values is less than 0.67?

This gets me the wrong answer however.
 
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How do you add normal distributions?
 
I think what the question is asking, is that 3 random numbers are chosen FROM a standard normal distribution. It's then asking what the chances are that their sum is less than 2.
 
Same thing.
The numbers are x,y, and z - their possible values are distributed normally with mean 0 and standard deviation 1.

the sum of them is s=x+y+z ... s has a range of possible values too.
You need to find how s is distributed, it's pdf, so you can find P(s<2). How do you add normal distributions?
 

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