>>1141002Fucking hell, are y'all retarted?
Three keys, we need two.
So:
- if first key doesn't work (0.25 chance), two other keys must work. So 0.25*0.75*0.75
- if first key works, only one key must work. Chance of one-key-of-two-working can be calculated two ways, either (0.75 + 0.25*0.75) or (1-0.25*0.25). So 0.75*(0.75 + 0.25*0.75)
Final answer:
In [1]: 0.75*(0.75 + 0.25*0.75) + 0.25*(0.75*0.75)
Out[1]: 0.84375
