Tính tổng sau bằng cách thuận tiện:
\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}.\)
.
Hướng dẫn giải:\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)
\(=(\frac{9}{10}+\frac{1}{10})+(\frac{7}{9}+\frac{2}{9})+(\frac{5}{8}+\frac{3}{8})+(\frac{4}{7}+\frac{3}{7})+(\frac{3}{5}+\frac{2}{5})\)
\(=1+1+1+1+1\)
\(=5.\)
