Đáp án:
`x=2011`
Giải thích các bước giải:
`x/2011 - 1/10 - 1/15 - ... - 1/120 = 5/8`
`↔ x/2011 - 2/20 - 2/30 - ... - 2/240 = 5/8`
`↔ x/2011 - (2/20 + 2/30 + ... + 2/240)= 5/8`
`↔ x/2011 - 2 (1/20 + 1/30 + ... + 1/240)=5/8`
`↔ x/2011 - 2 (1/(4×5) + 1/(5×6) + ... + 1/(15×16)) = 5/8`
`↔ x/2011 - 2 (1/4 - 1/5 + 1/5 - 1/6+ ... + 1/15 - 1/16) = 5/8`
`↔x/2011 - 2 (1/4 - 1/16) = 5/8`
`↔ x/2011 - 2 (4/16 - 1/16)=5/8`
`↔ x/2011 - 2 × 3/16 = 5/8`
`↔ x/2011 - 3/8 = 5/8`
`↔ x/2011 = 5/8 + 3/8`
`↔ x/2011 = 1`
`↔x=2011 ×1`
`↔x=2011`
Vậy `x=2011`
