Newsvendor model when demand is normal

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$$is called the critical fractile

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$$Suppose demand is normally distributed with mean

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$$and standard deviation

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$$k Calculate the critical fractile:

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$9$

$0$

$9$

$0$

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$9$

$$Find the corresponding

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value

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$1$

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$2$

$8$

$$Optimal Quantity

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$\backslash$times

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$2$

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$8$

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$$ie just for Normal distribution. How do i find the z

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value

$1$

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$2$

$8$

$$given this information without the confidence level. Whats the formula or technique please explain thanks