Đáp án + Giải thích các bước giải:
`A = \frac{1}{12} + \frac{1}{20} + \frac{1}{30} +...+ \frac{1}{506} + \frac{1}{552}`
`A = \frac{1}{3.4} + \frac{1}{4.5} + \frac{1}{5.6} +...+ \frac{1}{22.23} + \frac{1}{23.24}`
`A = \frac{1}{3} - \frac{1}{4} + \frac{1}{4} - \frac{1}{5} + \frac{1}{5} - \frac{1}{6} +...+ \frac{1}{22} - \frac{1}{23} + \frac{1}{23} - \frac{1}{24}`
`A = \frac{1}{3} - \frac{1}{24}`
`A = \frac{8}{24} - \frac{1}{24}`
`A = \frac{7}{24}`
Vậy `A = \frac{7}{24}`
