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Uses of mean, standard deviation and Z tables

  • Thread starter sazzlefrazzle
  • Start date
  • #1
sazzlefrazzle
Hey i was wondering if anyone could help me with this question at all? I don't have a clue about the calculations and would be grateful if it could be explained to me! I'm really struggling! Thanks

Some light emitting diodes are tested and a sample is found to have a mean lifetime of 2048 hours and a standard deviation of 40 hours. The manufacturer wants to give a guaranteed lifetime for the LED’s on the box so that only 2% of the bulbs will be returned for not lasting for the guaranteed lifetime. Using Z table standard normal distribution show your calculation giving the lifetime he should put on the box.
 

Answers and Replies

  • #2
exk
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0
The question is asking you to find the lifetime X such that the probability of failure P(F) is less then or equal to .02.
 
  • #3
HallsofIvy
Science Advisor
Homework Helper
41,794
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Do you know how to change from a normal distribution with mean [itex]\mu[/itex] and standard deviation [itex]\sigma[/itex] to the standard normal distribution? If not, why in the world are you doing a problem like this?
 

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