Distribution and Standard deviation

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Let $X$ be normally distributed with a mean of $105$ and standard deviation of $10$.

  1. What is the probability that $X > 112$?
  2. What value of $X$ does only the top $5\%$ exceed ?
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Not sure how to do this question

ok.

Using standardization that is

$$Z=\frac{X-\mu}{\sigma}$$

you can use Z-score to calculate probablities...

thus

$$P(X<112)=P\left(Z<\frac{112-105}{10}\right)$$

and obviously

$$P(X>112)=1-P(X<112)$$


The second question is an inverse Z-score problem...they give you the probability and you have to calculate the quantile