What is the probability that the second card drawn is a spade if the first card drawn is an ace?
1. 1st card drawn is not replaced.
2. 52 cards in a deck.
- Anonymous8 years agoBest Answer
(1/4) of the time the first card will be the spade Ace and the probability of the next card being a spade is (12/51)
(3/4) of the time the first card wqill be a different ace and the probability of the second card drawn being a spade is (13/51)
((1/4) * (12/51)) + ((3/4) * (13/51)) = (12 + 39) / 204) = (51 / 204) = (1/4) <----- Answer
This is intuitively obvious since (1/4) of aces are spades and (1/4) of non-aces are spades.
- ZantiLv 68 years ago
Hmm, are the other posters reading too much into this question?
If the first card is an ace, it could be the ace of spades (1/4 chance) or one of the other aces (3/4 chance). The probability that the next card is a spade is 1/4 - pulling an ace first has no effect on the result.
OK, I see Gerry has made a correction. :)
- SnacktimeLv 48 years ago
Consider the cases: if your ace is a spade, then you have 51 cards remaining, but only 12 of which are spades. Hence P(Spade) = 12/51
If your ace is not a spade, then you have 51 cards remaining and 13 spades remaining, hence P
- Elizabeth MLv 78 years ago
P(2S|1A) = P(1A and 2S)/P(1A) with obvious notation.
P(1A and 2S) = P(1A not S and2S)+P(1AS and 2S)
P(1A)=4/52 so answer=1/4
There's probably an easier method!