5/4-9/20+11/30-13/42+15/56-17/72+19/90=

5/4-9/20+11/30-13/42+15/56-17/72+19/90=
5/4-9/20+11/30-13/42+15/56-17/72+19/90=

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

11/10

1+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=11/10