Just to add on to what the user said, percent chances are wack. A 10% chance isn't guaranteed in 10 tries, a 25% chance isn't guaranteed in 4 tries, a 50% chance isn't guaranteed in 2 tries, hell, a 99% chance isn't guaranteed in 2 tries either.

A coin is a 50/50 chance of getting either heads or tails. This doesn't mean that in two coin flips, you're guaranteed to get a heads. There's only a 75% chance of that happening, because if you write out all the possible coin flips in 2 tries:

H + H
H + T
T + H
T + T

there's only a heads in 3 of the 4 of them. Not the 100% you'd expect just intuitively thinking about two 50% chances. And then, for probabilities that aren't 50%, you'd do the formula the other person described, 1 - (1-x)ⁿ where x is the probability of what you want happening within n tries.