数学算术题请人解决一下！！急急急急急！！！！！

貌似是这样
1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90
=1-(2+3)/(2*3)+(3+4)/(3*4)-(4+5)/(4*5)......(9+10)/(9*10)
=1-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)........+(1/9+1/10)
正的整理到一起，负的整理到一起
=1+(1/3+1/4+....1/10)-(1/2+1/3+....1/9)
=1+1/10-1/2
=3/5

1—5/6+12/7—20/9+30/11—42/13+56/15—72/17+90/19
=1-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)-(1/8+1/9)+(1/9+1/10)
=1-1/2+1/10
=3/5

九分之八