求助一道數學題pp exam 6

ai559031

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 people ranked vanilla first?

A. 2
B. 6
C. 14
D. 16
E. 24

ans. A

完全不知道該如何下手

ChrisYU924

six combinations:
V>C>S......[1];
V>S>C......[2];
C>V>S......[3];
C>S>V......[4];
S>V>C......[5];
S>C>V......[6];
therefore,
[4]+[6]=3/5*60=36;
[1]+[2]+[5]=1/10*60=6;
[1]+[2]+[3]=1/3*60=20;
so 2*([1]+[2])+[4]+[6]+[3]+[5]=36+6+20=62
therefore, [1]+[2]=2
choose A

ai559031

ChrisYU924 发表于 2016-6-30 17:15
six combinations:
V>C>S......[1];
V>S>C......[2];

好清楚！非常感謝

空军1号

ChrisYU924 发表于 2016-6-30 17:15
six combinations:
V>C>S......[1];
V>S>C......[2];

妈耶神仙