If I mix a 5 star unit with a 3 star unit, how many stars will the character have?

I mixed a 4 star unit with a 3 star unit, and I think it gave me a 3 star character. Would mixing a 5 star unit with a 3 star unit give me a 4 star character? Is there a % of chance that I keep my 5 stars when they mix? Any information on this would be great. Thanks!