125 20 44.4
分析:(1)把男生人数看作单位“1”,用1÷

解答即可;
(2)把男生人数看作单位“1”,用1-

解答即可;
(3)把分数理解成比,即女生和男生人数的比为4:5,则女生占总人数的

,化成百分数即可;
解答:(1)1÷

=

=125%;
(2)1-

=

=20%;
(3)

÷(1+

)=

≈44.4%;或4÷(4+5)≈44.4%;
答:男生人数是女生的125%,女生比男生少20%,女生占总人数的44.4%;
故答案为:125%,20%,44.4%.
点评:解答此题应根据分数除法的意义和把一个数是另一个数的几分之几理解成比,进行解答即可.