can someone clear up overpair

odds for me.

I always understood that say a pocket pair of 10s against say a pocket pair of 5s was about 89% to 11% favourite but looking on other sites they suggest the overpair is about 80 / 20 favourite.

Whilst I am no genius at working out the odds I always thought that the chance of the under pair hitting one of their remaining 2 cards was about 4.5% per card, pre flop they have 5 cards to come so 5 x 4.5% equates to 22% chance of them making trips, however I also have the same chance of hitting the 3rd 10 so this should half the odds making them only an 11% chance of winning.

Am I going wrong somewhere or are these other sites wrong?

I understand that possible straights, flushes, split pots can alter the odds a fraction but I am confused.

I just need to know, am I as unlucky as I think I am or are the odds only 4 to 1 in my favour of winning.

Thanks