a)  $1\frac{3}{4}:2\frac{3}{5}:1\frac{1}{2}=$ $\left(20\cdot 1\frac{3}{4}\right):\left(20\cdot 2\frac{3}{5}\right):\left(20\cdot 1\frac{1}{2}\right)=35:52:30$