请问最近数学机井上的一道题

helena0615

There are 1,200 respondents in a survey. And they are divided into three groups, such as A, B and C with percentage of 54%, 36% and 42% respectively (numbers may not be accurate). The percentage of A and B is 30%, what is the maximum number of C that is neither in A nor B.答案应该是312

请问这道题应该怎么做啊

rumblevan

是480 A和B一共30% A是54%B是36% 我觉得A和B的全局是60%（54+36-30） 1-60%=40% 而C占42% 我觉得C非A/B占最大就是40%
1200*40%=480

sysxy1987

The table gives three factors to be considered when choosing an Internet service provider and the percent of the 1,200 respondents to a survey who cited that factor as important.  If 30 percent of the respondents cited both “user-friendly” and “fast response time,” what is the maximum possible number of respondents who cited “bargain prices,” but neither “user-friendly” nor “fast response time?”

Factor	Percent of Respondents
User-friendly	56%
Fast response time	48%
Bargain prices	42%

 

画韦恩图，U+F+B-UF-UB-FB-2UFB=100% AND UF=30
所求=[B-UB-FB-2UFB]=100%+UF-U-F=100%+30%-56%-48%=26%
当B是已经确定的42%，如果UB or FB or 2UFB 有增加时候，整体[]将小于26%，因此，最大的可能就是26%。1,200*26%=312

CCAML

对于整体来说要 -2UFB, 但对于所要求的只要从B中减一次UFB呀。

sysxy1987

恩，如果这么考虑的话二楼的是对的，应该只要减去一次UFB的，那就应该用二楼的做法！

谢谢提醒了！