[求助]GMATPrep里的一道题

In a class of 30 students, 2 students did not borrow any books from the library, 12 students each borrowed 1 book, 10 students each borrowed 2 books, and the rest of the students each borrowed at least 3 books. If the average (arithmetic mean) number of books borrowed per student was 2, what is the maximum number of books that any single student could have borrow?

A.3
B.5
C.8
D.13
E.15

ans: D

没算出是13，不知道我是不是理解错了，请NN帮忙

能借最多书的情况是剩下的6个人中，有五个都是借3本

这样

12*1+10*2+5*3+n=2*30

解得n=13

thx

当时竟然做错了