1/55+2/55+3/55+.10/55-10/155-11/155-12/155.20/155=(1+2+3+...+10)/55-(10+11+12+...+20)/155=55/55-165/155=1-(1+10/155)=-2/31 9/14=1/( )+1/( )+1/( )+1/( ) =18/28=1/28+1/7+1/4+1/14