请教princeton中的一题

vivian12cn

A certain college has a total of 400 seniors, each majoring in exactly one of six subjects. A minimum of 20 seniors major in each of the six subjects, if three-quarters of the senior major in one of the four subjects, what is the greatest possible number of seniors majoring in one of the other two subjects?

我看不太懂题目的意思。请教各位。帮忙解释。答案是80

hohoo

400个大肆的分别只能修6门课，且每门课至少20人修，其中3/4的修了当中的四门，问剩下两门中最多一门课被主修的人数是多少？
400*1/4 = 100 修那两门， 因为至少20人修一门，所以至多100-20 ＝ 80