Answer to Question #311336 in Statistics and Probability for Ray

Question

$$P(X<85)=P(Z<\dfrac{85-\mu}{\sigma})=0.1$$ $$\dfrac{85-\mu}{\sigma}\approx-1.2815516$$ $$P(X<142)=P(Z<\dfrac{142-\mu}{\sigma})=0.65$$ $$\dfrac{142-\mu}{\sigma}\approx0.385320$$ $$\dfrac{85-\mu}{-1.2815516}=\dfrac{142-\mu}{0.385320}$$ $$\mu=\dfrac{85(0.385320)+142(1.2815516)}{0.385320+1.2815516}$$ $$\mu\approx128.8237$$ $$\sigma=\dfrac{142-128.8237}{0.385320}$$ $$\sigma=34.1957$$

Answer:

$\mu=129, \sigma=34$

Q- Where did you get the -1.2815516 and 0.385320?

Answer 1

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