Bài 1:
`\frac{(700×4+800):1,6}{(700×4+800):3,2}`
`=\frac{(700×4+800):\frac{8}{5}}{(700×4+800):\frac{16}{5}`
`=\frac{(700×4+800)×\frac{5}{8}}{(700×4+800)×\frac{5}{16}`
`=\frac{5}{8}:\frac{5}{16}`
`=\frac{5}{8}×\frac{16}{5}`
`=\frac{16}{8}`
`=2`
Bài 2:
$40$ % $+$ $x$ $+$ $x$ $×$ $20$ % $=$ $72$
$x$ $×$ $($ $40$ % $+$ $20$ % $)$ $=$ $72$
`x×\frac{60}{100}=72`
`x×\frac{3}{5}=72`
`x=72:\frac{3}{5}`
`x=72×\frac{5}{3}`
`x=\frac{72×5}{3}`
`x=\frac{360}{3}`
`x=120`