`E = 4/40 + 4/88 + 4/154 + ... + 4/4828`
`= 4/(5 . 8) + 4/(8 . 11) + 4/(11 . 14) + ... + 4/(68 . 71)`
`=> E/4 = 1/(5 . 8) + 1/(8 . 11) + 1/(11 . 14) + ... + 1/(68 . 71)`
`=> 3/4E = 3/(5 . 8) + 3/(8 . 11) + 3/(11 . 14) + ... + 3/(68 . 71)`
`= 1/5 - 1/8 + 1/8 - 1/11 + 1/11 - 1/14 + ... + 1/68 - 1/71`
`= 1/5 - 1/71 = 71/355 - 5/355 = 66/355`
`=> E = 66/355 ÷ 3/4 = 88/355`
Vậy `E = 88/355`.