A coin is tossed. find the probably that the result is heads

It is a 50% probability that it will land on heads.

there are 2 options for it to land on (heads or tails) and it will only land on 1 of them so we can show this by putting it into a fraction

1/2 or 1:2 or 0.5 or 50% whichever format you want to show it in