A weather forecast.
Pr(Windy given not Sunny) = Pr(Windy and not Sunny)/Pr(not Sunny) = 0.2/(1 - 0.3) = 0.2/0.7 which rounds to D 29%
20
The chair of the board of directors says, "There is a 50 percent chance this company will earn a profit, a 30 percent chance it will break even, and a 20 percent chance it will lose money next quarter".
Probably not
20 percent without condom
Not neccessarily, there's a 20% chance it can rain.
It means there is an 80 % chance it will rain and a 20% chance it wont. In other words, it means take your umbrella!
0.20 + 0.80*0.80
Usually about 20 or 30 kills
There is an 80% or 0.80 chance that it will not rain on Saturday
If you have unprotected sex for a year, you have a 20 percent chance of getting pregnant during each cycle.
I assume the probability is given a percent, or as odds, i.e. there's a 20% chance or 1 in 5 chance. You convert a percent by dividing by 100, 20% = 0.20, you convert odds by dividing the first number by the second, ie: 1/5 = 0.20.