`1/10 + 4/20 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 64/80 + 81/90`
`= 1/10 + 1/5 + 3/10 + 2/5 + 1/2 + 3/5 + 7/10 + 4/5 + 9/10`
`= 1/10 + 2/10 + 3/10 + 4/10 + 5/10 + 6/10 + 7/10 + 8/10 + 9/10`
`= (1/10 + 9/10) + ( 2/10 + 8/10) + ( 3/10 + 7/10 ) + ( 4/10 + 6/10) + 5/10`
`= 1 + 1 + 1 + 1 + 1/2`
`= 4 + 1/2`
`= 8/2 + 1/2`
`= 9/2`