2:4

2:4 simplifies to 1:2.

Reason: gcd(2,4) = 2; divide both terms by 2 → 2/2 : 4/2 = 1 : 2. Also 2/4 = 1/2 = 0.5 (or 50% if you think in percent).

If you meant something else with 2:4, tell me the context.