Đáp án:
Giải thích các bước giải:
-Ta có: `1/6 = 1.2/6.2 = 2/12`
`1/7 = 1.2/7.2 = 2/14`
..................................
`1/15 = 1.2/15.2 = 2/30`
`→ A = 2/11 + 2/12 + 2/13 + 2/14 +................+ 2/29 + 2/30`
-Ta có: `2/11 > 2/30; 2/12 > 2/30; 2/13 > 2/30; 2/14 > 2/30; ............ ; 2/29 > 2/30; 2/30 = 2/30`
`→ A > 2/30 + 2/30 + 2/30 + 2/30 +.........+ 2/30 + 2/30`
`→ A > 2/30 . [ ( 30 - 11 ) : 1 + 1 ]`
`→ A > 2/30 . 20`
`→ A > 4/3`
Vậy `A > 4/3`