Cho M=(21/31 + -16/7 ) + (44/53 + 10/31) + 9/53

* Hướng dẫn giải

Đáp án cần chọn là: D

$\begin{array}{l}M=\left(\frac{21}{31}+\frac{-16}{7}\right)+\left(\frac{44}{53}+\frac{10}{31}\right)+\frac{9}{53}\\ M=\frac{21}{31}+\frac{-16}{7}+\frac{44}{53}+\frac{10}{31}+\frac{9}{53}\\ M=\left(\frac{21}{31}+\frac{10}{31}\right)+\left(\frac{44}{53}+\frac{9}{53}\right)+\frac{-16}{7}\\ M=1+1+\frac{-16}{7}\\ M=2+\frac{-16}{7}\\ M=\frac{-2}{7}\end{array}$

$\begin{array}{l}N=\frac{1}{2}+\frac{-1}{5}+\frac{-5}{7}+\frac{1}{6}+\frac{-3}{35}+\frac{1}{3}+\frac{1}{41}\\ N=\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{3}\right)+\left(\frac{-1}{5}+\frac{-5}{7}+\frac{-3}{35}\right)+\frac{1}{41}\\ N=\frac{3+1+2}{6}+\frac{\left(-7\right)+\left(-25\right)+\left(-3\right)}{35}+\frac{1}{41}\\ N=1+\left(-1\right)+\frac{1}{41}\\ N=\frac{1}{41}\end{array}$