1. 40比（ 40又3/8）少3/8
120比（ 119又3/4）多1/4
2. 1/2+1/6+1/12+1/20+1/30+1/42+1/52+1/72+1/90
=1/（1*2）+1/(2*3)+1/(3*4)+...+1/(8*9)+1/(9*10)
=(1/1-1/2)+(1/2-1/3)+(1/3-1/4)+...+(1/8-1/9)+(1/9-1/10)
=1-1/10
=9/10
3.暂时还没想到,不好意思哦.