prep ps1-105&106

foreversun99

105.    11075-!-item-!-187;#058&007490
Two water pumps, working simultaneously at their respective constant rates, took exactly 4 hours to fill a certain swimming pool.  If the constant rate of one pump was 1.5 times the constant rate of the other, how many hours would it have taken the faster pump to fill the pool if it had worked alone at its constant rate?
(A) 5
(B)  
(C)  
(D) 6
(E)  

題目給的選項不完整,所以得靠自己解出來,不 知有哪位高手能幫忙解出來一下?  感謝
解答給E(?)

106.    11122-!-item-!-187;#058&007588
If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than 2.5 standard deviations from the mean?

(A) 12.0
(B) 13.5
(C) 17.0
(D) 23.5
(E) 26.5
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【答案】 A

不太了解題目及解答版的思路 不知有誰能幫忙解釋一下?

Simon88

105应该是20/6吧

foreversun99

請問您是如何算出的呢?

BESIDES,從哪句看出106題是在問 NOT between 12.5 and 27.5?

zjq3088

105应该是20/3