Bạn tham khảo
`A`= `3/10+3/11+3/12+3/13 +3/14`
Ta có : ` 3/15 + 3/15 + 3/15 +...+3/15 = 15/15 =1`
Mà
`3/10>3/15 , 3/11 > 3/14 , 3/12>3/15`
`3/13>3/15,3/14>3/15`
Vậy `A>1`
Ta lại có :
`3/11>3/10 , 3/12>3/10, 3/13>3/10,3/14>3/10`
`=> 3/10+3/11+3/12+3/13 +3/14> 3/10+3/10 +3/10+3/10+3/10 `
Mà` 3/10+3/10 +3/10+3/10+3/10 =3/2<2`
Vậy `1<A<2( đpcm)`