Honestly you dont need no formula too tell you if u have a better chance or not ,
lets say ur stats are
80 attack / 90 strength / 70 defence
ur oppenent
83 attack / 90 strength / 70 defence
hes gonna be hitting more often just cuz of his attack levels , but you still have a chance of killing him if he hits 0's its all about luck unless the other person is like 5 lvls above you then your bound to loose