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.

4 Answers

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  • Anonymous
    8 years ago
    Best 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.

    .

  • Zanti
    Lv 6
    8 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. :)

  • 8 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

    (spade) 13/51.

  • 8 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)

    = (3/52)(13/51)+(1/52)(12/51)=1/52

    P(1A)=4/52 so answer=1/4

    There's probably an easier method!

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