(1 )每天1/13 ,5天5/13
(2 )3+4+5=12 ,每段各占3/12=1/4,4/12=1/3 ,5/12
(3 )900/(300+900)=3/4
(4 )因为3/4小于4/5小于小于5/6,所以王师傅最快,张师傅最慢