Tìm x biết: a) 2 1/4 x - 9 1/4 = 20 b) 6 2/9 x + 3 10/27 = 22 1/7

* Hướng dẫn giải

a)

$\begin{array}{l}2\frac{1}{4}x-9\frac{1}{4}=20\\ \frac{9}{4}x-\frac{37}{4}=20\\ \frac{9}{4}x=20+\frac{37}{4}\\ \frac{9}{4}x=\frac{117}{4}\\ x=\frac{117}{4}:\frac{9}{4}\\ x=13.\end{array}$

b)

$\begin{array}{l}6\frac{2}{9}x+3\frac{10}{27}=22\frac{1}{7}\\ \frac{56}{9}x+\frac{91}{27}=\frac{155}{7}\\ \frac{56}{9}x=\frac{155}{7}-\frac{91}{27}\\ \frac{56}{9}x=\frac{3548}{189}\\ x=\frac{3548}{189}:\frac{56}{9}\\ x=3\frac{5}{294}.\end{array}$