Tính nhanh: A=1/3 - 3/4 - (-3/5)+1/72 - 2/9 - 1/36 - 1/15

* Hướng dẫn giải

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