Tính tổng các phân số: A = 3/2.5 + 3/5.8 + 3/8.11 ++ 3/92.95
Tính tổng các phân số: \[A = \frac{3}{{2 \times 5}} + \frac{3}{{5 \times 8}} + \frac{3}{{8 \times 11}} + ... + \frac{3}{{92 \times 95}}\].
\[A = \frac{3}{{2 \times 5}} + \frac{3}{{5 \times 8}} + \frac{3}{{8 \times 11}} + ... + \frac{3}{{92 \times 95}}\]
\[ = \frac{{5 - 2}}{{2 \times 5}} + \frac{{8 - 5}}{{5 \times 8}} + \frac{{11 - 8}}{{8 \times 11}} + ... + \frac{{95 - 92}}{{92 \times 95}}\]
\( = \frac{1}{2} - \frac{1}{5} + \frac{1}{5} - \frac{1}{8} + ... + \frac{1}{{92}} - \frac{1}{{95}}\)
\( = \frac{1}{2} - \frac{1}{{95}} = \frac{{93}}{{190}}\)