有冇人可以指教下我點計條Probability法最好
2011-10-31 12:32 am
The daily income of a group of 10,000 persons is found to be normally distributed with mean $750 and standard deviation of $50.(a) Find the expected number of persons with income fewer than $650 or more than $830. (b) What is the lowest income among the richest 250 persons?(c) What are the properties of the normal distribution?
回答 (1)
2011-10-31 5:26 am
✔ 最佳答案
(a) P(X<650) + P(X>830)= P(Z< (650-750)/50) + P(Z> (830-750)/50)
= P(Z< -2) + P(Z>1.6)
= 0.0228 + 0.0548
= 0.0776
expected number of persons is 776
(b) 250/10000 = 0.025
P(Z > 2.81) = 0.025
So, X = 2.81 * 50 + 750 = 890.5
(c)(i) bell shape (ii) mean = median = mode
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原文連結 [永久失效]:
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