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 $423 and unknown standard deviation. If the proportion of earnings over $452 is 28%, find the standard deviation. Answer only up to two digits after decimal. ( )

X is a normal random variable with mean μ and standard deviation σ. Then P( μ− 1.7 σ ≤ X ≤ μ+ 2.1 σ) =? Answer to 4 decimal places. ( )

If Z is a standard normal random variable, find c such that P(−c ≤ Z ≤ c) = 0.91. [Answer to 2 decimal places] ( )

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orchestra answered 1 year ago

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