P2-DS-93

[Huang Hsin-Yi]

93. 8624-!-item-!-187;#058&006485
The lifetimes of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m + d ?

(1) 68 percent of the distribution lies in the interval from m - d to m + d, inclusive.

(2) 16 percent of the distribution is less than m - d.

Ans:D

這個題目,我是看了半天都還不知怎樣下手

[amazingslim]

以平均數m為中點
(1) m - d to m + d:68%
=>m + d:34%
=>大於m + d:16%

(2)<m - d:16%
=>m - d:34%
=>m + d:34%
=>大於m + d:16%

[Huang Hsin-Yi]

大師,怎麼辦,我還是看不懂為什麼要這樣解
還請略指一二

[aqboy[origen]]

題目說 a distribution that is symmetric about the mean m. 分配是左右對稱的, 故以平均數M為中點解題,這樣應該清楚一點

[Huang Hsin-Yi]

懂了!!謝謝

[yilingsky]

16% 怎麼來的???

[sunnyblue13s]

50%-34% = 16% or (100%-68%)/2 = 16%