Bài 1:
$1,2(5)+3,(45)-\frac{17}{7}$
$=\frac{113}{90}+\frac{38}{11}-\frac{17}{7}$
$=\frac{8701}{6930}+\frac{23940}{6930}-\frac{16830}{6930}$
$=\frac{8701+23940+16830}{6930}$
$=\frac{49471}{6930}$
Bài 2:
$0,(17).0,3=2,(3).x$
$\frac{17}{99}.\frac{3}{10}=\frac{7}{3}.x$
$\frac{7}{3}.x=\frac{17}{330}$
$x=\frac{17}{330}:\frac{7}{3}$
$x=\frac{17}{770}$