b2bt wrote:
I still don't get it. Does the question means that he gets to see the game only if it doesn't rain at all? On monday and on tuesday too?
OE by Veritas Prep
E. Two sequences work for Chris to attend the game: Either it doesn't rain on Monday night (60% chance) or it does rain on Monday night but then not on Tuesday night (a 40% chance that it doesn't rain Monday, then a 60% chance it doesn't rain Tuesday). The first probability is 3/5, and the second is (2/5)(3/5) = 6/25. Converting to find a common denominator, that's 15/25 + 6/25 = 21/25, which converts to 84%.
Alternatively, you could look at it by seeing that the only way he cannot see the game is that it rains both nights, a 40% * 40% = 16% sequence. If 16% of the outcomes don't work for him, then 84% do, again making the answer E.
What if it doesn't rain on Monday but rains on Tuesday?
The question says, "...Chris receives tickets to a baseball game that will be played at 7pm on the next evening that it does not rain"
So if it does not rain on Monday evening, the game will be played on Monday evening and will be over. After that, what happens on Tuesday is immaterial. The probability of no rain on Monday is 3/5.
If it does rain on Monday, the game will not be played on Monday. This probability is 2/5. Then if it does not rain on Tuesday evening, the game will take place on Tuesday evening. Hence probability of game on Tuesday evening is (2/5)*(3/5).
In these two cases, Chris will see the game. Total Probability = 3/5 + (2/5)*(3/5) = .84
If it rains on Tuesday too, then the game will be shifted by another day. In that case, Chris will not be able to see the game since he will fly out on Wednesday morning.