SOLUTION: A local manufacturer wants to know how long to guarantee her toasters. A random sample of 16 toasters has an average lifespan of 1,000 hours with a standard deviation of 200 hours.

Question 233878: A local manufacturer wants to know how long to guarantee her toasters. A random sample of 16 toasters has an average lifespan of 1,000 hours with a standard deviation of 200 hours. If she doesn't want to replace any more than 10% of the toasters, for how long should she gaurantee her toasters?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A local manufacturer wants to know how long to guarantee her toasters. A random sample of 16 toasters has an average lifespan of 1,000 hours with a standard deviation of 200 hours. If she doesn't want to replace any more than 10% of the toasters, for how long should she gaurantee her toasters?
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Find the z-value associated with a left tail of 10%.
I used my TI-84 calculator to get:
invNorm(0.10) = -1.2816
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Find the "x" value associated with that z value
using x = zs + u
x = -1.2816*200 + 1000
x = 743,69 hours
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She should guantee them for around 745 hrs. of use
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Cheers,
Stan H.

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