煩請統計高手來救火！！

煩請大大解題，最好能附上詳細說明及算法。

A、The weight of a human joint replacement part is normally distributed

with a mean of 2 ounces and a standard deviation of 0.05 ounce.

1.What is the probability that a part weights more than 2.10 ounces？

2.What must the standard deviation of weight be for the company to 90%

of its parts are less than 2.10 ounces？

祝：安康順心  百事可樂

[ 本帖最後由 max1130 於 2007-12-25 11:18 編輯 ]

1.Cumulative Distribution Function

Normal with mean = 2 and standard deviation = 0.05

  x  P(&nbsp;X&nbsp;<=&nbsp;x&nbsp;)
2.1     0.977250
1 - 0.977250 = 0.022750  →   2.275%           Ans : 2.275%

2.  90%之累積機率  查表Z值為1.28
      (2.10-2)/σ = 1.28    →   σ =0.078125        Ans : 0.078125