Tìm x, biết: a) 13/4 + 9/10 = 83/x b) x = 2/5 + 1/4 + -1/3

* Hướng dẫn giải

a) $\frac{13}{4}+\frac{9}{10}=\frac{83}{x}\iff \frac{13.5+9.2}{20}=\frac{83}{x}$$\iff \frac{83}{20}=\frac{83}{x}\iff x=20$

b) $x=\frac{2}{5}+\frac{1}{4}+\frac{-1}{3}$$\iff x=\frac{2.12+1.15+(-1).20}{60}\iff x=\frac{19}{60}$