`A = ( 1 - 1/2^2 ) . ( 1 - 1/3^2 ) ............... ( 1 - 1/100^2 )`
`A = 3/3^2 . 8/3^2 .................... 9999/100^2`
`A = 3/2 . 4/3 ............ 101/100`
`A = 1/2 . 101/100`
`A = 101/200`
-Ta có `A = 101/200 > 100/200 = 50%`
→ `A > 50%`
-Ta có: `A = 101/200 < 102/200 = 51%`
→ `A < 51%`
Vậy `50% < A < 51%`