5/4-9/20+11/30-13/42+15/56
=5/4-9/(4*5)+11/(5*6)-13/(6*7)+15/(7*8)
=5/4-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)
=1+1/8
=9/8 5/4-9/20+11/30-13/42+15/56
=5/4-9/(4*5)+11/(5*6)-13/(6*7)+15/(7*8)
=5/4-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)
=1+1/8
=9/8