1/2x1/3+1/3-1/4+1/4x1/5

* Hướng dẫn giải

$\frac{1}{2}$x$\frac{1}{3}$+$\frac{1}{3}$-$\frac{1}{4}$+$\frac{1}{4}$x$\frac{1}{5}$

= $\frac{1}{2}$-$\frac{1}{3}$+$\frac{1}{3}$-$\frac{1}{4}$+$\frac{1}{4}$-$\frac{1}{5}$

=$\frac{1}{2}$-$\frac{1}{5}$

=$\frac{3}{10}$. ($\frac{1}{2}$x$\frac{1}{3}$= $\frac{1}{2}$x3)