`5^2/1.3 + 5^2/3.5 + 5^2/5.7 + .... + 5^2/103.105`
`= ( 2/1.3 + 2/3.5 + 2/5.7 + .... + 2/103.105 ) : 2 . 5^2`
`= ( 1/1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ... + 1/103 - 1/105 ) : 2 . 25`
`= ( 1/1 - 1/105 ) : 2 . 25`
`= 104/105 : 2 . 25`
`= 52/105 . 25`
`= 260/21`