To the peeps who asked how 10 attempts at 4/5 chance of failure can yeild a 89% chance of being successful:
4/5 ^ 10 =
10.73% chance of NOT getting any success.
As chance of not getting any succes at all and chance of getting (any amount of) succes must add up to 100%, then it follows
100 - 10.73 = 89.27% chance of getting one or more succeses.