(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

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?

2. Relevant equations

sd=standard deviation

u=mean

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

3. 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!

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# Homework Help: Normal distribution problem

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