Weakly earnings on a certain import venture are approximately normally distributed with a known mean of...

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Weakly earnings on a certain import venture are approximately normally distributed with a known mean of...

Weakly earnings on a certain import venture are approximately normally distributed with a known mean of $386 and unknown standard deviation. If the proportion of earnings over $419 is 25%, find the standard deviation. Answer only up to two digits after decimal.

math Statistics-And-Probability

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Answer 1

Answer #1

We have given,

P[X>419]=0.25

Therefore,

$P[Z>\frac{419-386}{\sigma}]=0.25$

Now,

$\frac{419-386}{\sigma}=0.67$ ...............by using Z table or Excel =NORMSINV(1-0.25)

$=>\sigma=49.25$

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Answer 2

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