OK, I’ll take one last crack at explaining this to you Jen. I know you don’t like me, but please try to actually listen to what I’m saying this time. And hopefully this post doesn’t get deleted. :roll:
Suppose I flip a coin. What are the odds it comes up heads? Well, I hope we can agree that its 1/2.
Now, suppose I flip a coin on Monday, Wednesday, and Friday. What are the odds of the coin coming up heads on Friday?
Thus far you have reasoned like this: the odds of the coin coming up heads is 1/2, but we must also take into account what day of the week it is. There is only 1 “correct” day of the week (Friday) in which a coin gets flipped, while there are 2 “incorrect” days (Monday, and Wednesday). So there is only a 1/3 chance of it being Friday when the coin is flipped. Therefore, the odds that the coin comes up heads on Friday is (1/2)*(1/3) = 1/6.
Correct?
No. Here’s why:
What you’re trying to do is find the joint probability of two events using conditional probabilities. The problem is, you have the conditional backwards. See, we’re not deciding whether to flip a coin, and then assigning the result of the flip randomly to a Monday, Wednesday, or Friday. So we don’t want to know the probability of it being Friday, given that the coin is flipped. Instead, we’re seeing what day of the week it is, and then determining if the coin gets flipped or not based on whether or not it’s a Monday, Wednesday, or Friday. Thus, we want to know the probability of flipping a coin, given that it is Friday.
Of course, the probability of flipping a coin, given that it is Friday is equal to 1, since it’s stipulated that a coin always gets flipped on a Friday. So, the joint probability of flipping a coin on friday and flipping heads is: (1)*(1/2) = 1/2.
Do you see the difference? And do you see that you’re making the same mistake when calculating the odds of getting super subs?
We don’t want to know the odds of it being the “correct” nation, given that super subs has been discovered, we want to know the odds of super subs being discovered, given that it’s the “correct” nation.