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Normal distribution problem

  • Thread starter beanryu
  • Start date
  • #1
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Homework Statement


Plastic rods are cut into nominal length of 6 inches. Actual lengths are normally distributed about a mean of 6 inches and their standard deviation is 0.06 inch.

Question: To what value does the standard deviation need to be reduced if 99% of the rods must be within tolerance?

Homework Equations


sd=standard deviation
u=mean
P(a<X<=b)=F((b-u)/(sd))-F((a-u)/(sd))

The Attempt at a Solution


since they want the possibility of rods to be between u+sd and u-sd to be 0.99, b=u+sd and a=u-sd
and the equation will become
P(a<X<=b)=F((u+sd-u)/(sd))-F((u-sd-u)/(sd))
F(1)-F(-1) doesn't equal to 0.99.

Am I misinterpreting the word tolerance?
I dont know what else to try... please help thank you!
 
Last edited:

Answers and Replies

  • #2
92
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nevermind i misread the problem...
 

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