$a)$

$\frac{3}{10}=0,3$

$\frac{41}{100}=0,41$

$\frac{3}{100}=0,03$

$\frac{123}{1000}=0,123$

$\frac{12}{1000}=0,012$

$\frac{3}{1000}=0,003$

 

$b)$

$1\frac{5}{10}=1,5$

$1\frac{51}{100}=1,51$

$2\frac{5}{100}=2,05$

$3\frac{512}{1000}=3,512$

$10\frac{12}{1000}=10,012$

$200\frac{2}{1000}=200,002$