Tính nhanh:

Câu hỏi: Tính nhanh: $A = \frac{1}{3} - \frac{3}{4} - (- \frac{3}{5}) + \frac{1}{72} - \frac{2}{9} - \frac{1}{36} + \frac{1}{15}$

Đáp án

- Hướng dẫn giải

$\begin{array}{l} A = \frac{1}{3} - \frac{3}{4} - (- \frac{3}{5}) + \frac{1}{72} - \frac{2}{9} - \frac{1}{36} + \frac{1}{15} \\ = \frac{1}{3} - \frac{3}{4} + \frac{3}{5} + \frac{1}{72} - \frac{2}{9} - \frac{1}{36} + \frac{1}{15} \\ = (\frac{1}{3} + \frac{3}{5} + \frac{1}{15}) + (- \frac{3}{4} - \frac{2}{9} - \frac{1}{36}) + \frac{1}{72} \\ = (\frac{5}{15} + \frac{9}{15} + \frac{1}{15}) + (- \frac{27}{36} - \frac{8}{36} - \frac{1}{36}) + \frac{1}{72} \\ = 1 - 1 + \frac{1}{72} \\ = \frac{1}{72} \end{array}$