Đặt ` A= 1/99.97 - 1/97.95 - 1/95.93 -...-1/5.3 - 1/3.1`
`A = -1/1.3 - 1/3.5 -...- 1/93.95 - 1/95.97 + 1/97.99`
`A= -(1/1.3 + 1/3.5 +....+1/93.95 + 1/95.97 - 1/97.99)`
`2A= -( 2/1.3 + 2/3.5 + ...+ 2/95.97 - 2/97.99)`
`2A= -( 1/1 - 1/3 + 1/3 -1/5 +...+1/95 - 1/97 - 1/97 -1/99)`
`2A= -( 1/1 - 1/97 -1/97 - 1/99)`
`2A= -1 + 1/97 + 1/97 -1/99`
`A= ( -1 + 1/97 + 1/97 - 1/99) :2`
`A=-4751/9603`
Vậy `A= -4751/9603`