One-in-three chance vs One-third chance
There are 3 doors.
Behind the doors, two lambs and one porche.
If you are lucky, you can get a porche.
You can choose only one door.

1.You have one-in-three chance
2.You have one-third chance.

Can I use both sentences?

Question

One-in-three chance vs One-third chance
There are 3 doors.
Behind the doors, two lambs and one porche. 
If you are lucky, you can get a porche.
You can choose only one door.

1.You have one-in-three chance
2.You have one-third chance.

Can I use both sentences?

Answer

1. You have a one-in-three chance. (or "You have 33% chance.")

You can say "You have one-third of a chance," but it sounds very awkward. That construction is most often used in the idiom "give (someone) half a chance," meaning give someone even a very small opportunity.
- You'll find that he's a really great guy, if you just give him half a chance.
- I tried to beat him at tennis, but he's too much better than I am - I never even had half a chance.