3,57:1,7

To simplify the ratio 3.57:1.7, you can divide both numbers by 1.7:

\[ \frac{3.57}{1.7} \approx 2.1 \]

Thus the ratio simplifies to approximately 2.1:1.

If you want to express it in whole numbers, you can scale it up by multiplying both parts by 10, which gives you 21:10.

Therefore, the ratio 3.57:1.7 can be expressed as 21:10.