`A=55/(11xx16)+55/(16xx21)+55/(21xx26)+55/(26xx31)+55/(31xx36)+55/(36xx41)`
`A=11xx(5/(11xx16)+5/(16xx21)+5/(21xx26)+5/(26xx31)+5/(31xx36)+5/(36xx41))`
`A=11xx(1/11-1/16+1/16-1/21+1/21-1/26+1/26-1/31+1/31-1/36+1/36-1/41)`
`A=11xx(1/11-1/41)`
`A=11xx(41/(541)-11/(541))`
`A=11xx30/451`
`A=30/41`
$\text{Vậy}$`A=30/41.`