【谢谢坛友们！已解决】求助一道官网prep第六套的数学题

浪逐曲奇 · 发表于 2019-10-5 18:04:18

谢谢大家来看这个帖子~ 一道PS题。这道题我蒙对了A

，但是我不知道2是怎么算出来的，所以想向各位坛友求助，谢谢大家啦！！

In amarketing survey, 60 people were asked to rank three flavors of ice cream,chocolate, vanilla, and strawberry, in order of their preference. All 60 peopleresponded, and no two flavors were ranked equally by any of the peoplesurveyed. If of the people rankedvanilla last, of them ranked vanillabefore chocolate, and of them rankedvanilla before strawberry, how many people ranked vanilla first?

不清楚为什么A对。没理解这道题

A. 2

6

14

16

24

等到昏迷的兔子 · 发表于 2019-10-6 16:26:11

LZ你题目没打全吧

“In a marketing survey, 60 people were asked to rank three flavors of ice cream, chocolate, vanilla and strawberry, in order of their preference. All 60 people responded, and no two flavors were ranked equally by any of the people surveyed. If 3/5 of the people ranked vanilla last, 1/10 of them ranked vanilla before chocolate, and 1/3 of them ranked vanilla before strawberry, how many of them ranked vanilla first?”

等到昏迷的兔子 · 发表于 2019-10-6 16:40:38

题目问有多少人把香草味排第一。
第一个条件“3/5 of the people ranked vanilla last”，
可以知道36个人把香草味排最后（也就是第三），也就是说有24（60-36=24）个人把香草味要么排第一，要么排第二。

当香草味排第一的时候，它一定排在草莓味和巧克力味之前，对不对？

第二个条件“1/10 of them ranked vanilla before chocolate”，“1/3 of them ranked vanilla before strawberry”
可以知道有6个人把香草味排在巧克力味前面，有20个人把香草味排在草莓味前面。

这个时候可以借助文氏图，S代表只排在草莓前面，C代表只排在巧克力前面，交集就是排在两者前面，也就是排第一，设交集是X，
那么根据第一个条件可以知道S+C+X=60-36=24，
根据第二个条件可以知道S+X=6, C+X=20,

求出X=2

浪逐曲奇 · 发表于 2019-10-6 16:45:50

等到昏迷的兔子发表于 2019-10-6 16:26
LZ你题目没打全吧

“In a marketing survey, 60 people were asked to rank three flavors of ice cream, ...

啊！现在发现了是的从官网复制粘贴过来结果数字没了

。。

浪逐曲奇 · 发表于 2019-10-6 16:49:07

等到昏迷的兔子发表于 2019-10-6 16:40
题目问有多少人把香草味排第一。
第一个条件“3/5 of the people ranked vanilla last”，
可以知道36个人 ...

给您打call！！好厉害୧(๑•̀◡•́๑)૭ 非常感谢！！

等到昏迷的兔子 · 发表于 2019-10-6 16:50:20

浪逐曲奇发表于 2019-10-6 16:49
给您打call！！好厉害୧(๑•̀◡•́๑)૭ 非常感谢！！

不客气~

【谢谢坛友们！已解决】求助一道官网prep第六套的数学题

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