Tính nhanh A = 4/15 . 1/3 . 15/20 B = -5/8 . -12/29 . 8/-10 .29/5

* Hướng dẫn giải

$\begin{array}{l}A=\frac{4}{15}.\frac{1}{3}.\frac{15}{20}\\ A=\frac{\mathrm{4.1.15}}{\mathrm{15.3.20}}=\frac{1}{15}\end{array}$

$\begin{array}{l}B=\frac{-5}{8}.\frac{-12}{29}.\frac{8}{-10}.\frac{29}{5}\\ B=\frac{\left(-5\right).\left(-12\right)\mathrm{.8.29}}{\mathrm{8.29.}\left(-10\right).5}=\frac{-6}{5}\end{array}$