`E = (1/99 + 2/98 + 3/97 + ... + 99/1)/(1/2 + 1/3 + 1/4 +... + 1/100)`
`Tử số = 1/99 + 2/98 + 3/97 + ... + 98/2 + 99/1`
`= 1 + 1/99 + 1 + 2/98 + 1 + 3/97 + 1 + ... + 98/2 + 1`
`= 100/100 + 100/99 + 100/97 + ... + 100/2`
`= 100.(1/100 + 1/99 + 1/97 + ... + 1/2)`
`Mẫu số = 1/2 + 1/3 + 1/4 +... + 1/100`
`= 1/100 +1/99 + 1/97 + ... + 1/2`
`⇒ E = (100.(1/100 + 1/99 + 1/97 + ... + 1/2))/ (1/100 +1/99 + 1/97 + ... + 1/2)`
`⇒ E = 100`
`F = (94 - 1/7 - 2/8 - 3/9 - ... - 94/100)/(1/35 + 1/40 + 1/45 + ... + 1/500)`
`Tử số = 94 - 1/7 - 2/8 - 3/9 - ... - 94/100`
`= -1/7 + 1 - 2/8 + 1 - 3/9 + 1 - ... - 94/100 + 1`
`= 6/7 + 6/8 + 6/9 + ... + 6/100`
`= 6. (1/7 + 1/8 + 1/9 + ... + 1/100)`
`= 6. 5. 1/5. (1/7 + 1/8 + 1/9 + ... + 1/100)`
`= 6. 5. (1/35 + 1/40 + 1/45 + ... + 1/500)`
`= 30. (1/35 + 1/40 + 1/45 + ... + 1/500)`
`Mẫu số = 1/35 + 1/40 + 1/45 + ... + 1/500`
`⇒ F = (30. (1/35 + 1/40 + 1/45 + ... + 1/500))/(1/35 + 1/40 + 1/45 + ... + 1/500)`
`⇒ F = 30`
`⇒ 2F = 30. 2 = 60`
`⇒ E - 2F = 100 - 60 = 40`
`Vậy E - 2F = 40`
