Q14:

Of all the students in a certain dormitory, 1/2 are first-year students and the rest are second-year students. If 4/5 of the first-year students have not declared a major and if the fraction of second-year students who have declared a major is 3 times the fraction of first-year students who have declared a major, what fraction of all the students in the dormitory are second-year students who have not declared a major?

A. 1/15

B. 4/15

C. 1/3

D. 2/5

请教解题思路!谢谢!!!

我有思路,但是不知道哪里出问题了,算出来和哪个选项都不一样.

你就根据它题目说的,一个条件一个条件的把它能得出得结论写下来.

first year 4/5 not then 1/5 yeah

second year 3/5 yeah then 2/5 not

first year and second year 各一半

所以 (2/5)/2=1/5

怎么算出个1/5来啊.我哪里有问题啊?情纠正.

俺算的也是1/5,思路也和你的一模一样!

我也不知道自己错在哪里,郁闷呀!