0,5:2

Interpretation: 0,5:2 is the ratio 0.5 to 2.

• Remove decimals: multiply by 10 → 5:20
• Simplify by gcd 5 → 1:4

So the simplest form is 1:4 (also 0.25:1 or 1:4).

Note: If you actually meant 0.5 ÷ 2, that equals 0.25.