Gaussian PDF: Probability of P(x), Usable Shafts %

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Discussion Overview

The discussion revolves around calculating probabilities using the Gaussian probability density function (PDF) for two questions related to normal distributions. The first question involves determining various probabilities for a Gaussian distribution with specified parameters, while the second question focuses on the percentage of usable shafts in a manufacturing process based on their diameter distribution.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • Post 1 presents two questions regarding Gaussian distributions, asking for specific probabilities and the percentage of usable shafts based on given parameters.
  • Post 2 emphasizes the need for participants to show their working and suggests that converting to a standard normal distribution is essential for determining probabilities.
  • Post 3 calculates the z-score for the second question and expresses confusion about using the z-table, arriving at a percentage of usable shafts but questioning its correctness.
  • Post 4 acknowledges the reasonableness of Post 3's answer for the second question and advises following a similar approach for the first question, suggesting the use of z-scores and reference tables.

Areas of Agreement / Disagreement

Participants generally agree on the method of using z-scores to find probabilities, but there is no consensus on the correctness of the calculations or the answers to the first question.

Contextual Notes

There are unresolved steps in calculating probabilities for the first question, and participants have not fully clarified their assumptions regarding the use of z-tables.

Who May Find This Useful

Students or individuals interested in understanding Gaussian distributions, probability calculations, and the application of normal distribution in practical scenarios may find this discussion useful.

axnman
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Que. 1 Consider a Gaussian PDF with µ = 20, σ = 30, a = 50 and b =80. Determine i)Probability that P(x>b)
ii)P(x ≤ b)
iii)P(x ≤ - b)
iv)P(a ≤ x ≤ b)


Que. 2 In a certain manufacturing process only shafts whose diameters are less than 1.5 inches can be used. Given the shaft diameters are normally distributed with mean (µ) 1.490 inches and standard deviation (σ) 0.005 inches, determine the percentage of shafts that are usable.
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We can't just give you the answers...you need to show some working
Do you know how to turn a normal distribution into a standard normal distribution?
That is always the key to determining probabilities

You have all the information you'll need once you scale "a" and "b" correctly using the mean and standard deviation given

If you don't know how to manipulate the figures then i'll give you some hints
 
z = (X - µ ) / σ...am talking @ que. 2...This way z = (1.5-1.49) / 0.005 = 2...Then i get confused as i have to look into the tables...I get 0.0228...hmmm so well the answer should be 100 - 0.0228 % of shafts = 97.72%...Is that correct?

Q 1 am still trying...
 
Your answer to q2 looks pretty reasonable

For q1, follow the same lines as you did for q2
i.e. find z, then look up phi(z) in tables. Draw a bell curve if you have to etc.
 

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