If 2 cards are drawn from a normal deck of 52 cards, what is the probability that both cards will be spades?
1
Expert's answer
2012-04-03T07:29:51-0400
There 1/4*52 spades in the deck.Probability to pick a spade taking single card is 1/4. Due to multiplication rule probability to pick two cards-spades is 1/4*1/4=1/16
In fact this question is a little bit tricky. If we consider drawing
one card, putting it back in the deck, regardless if it is a spade or
not, then reshuffling the deck and drawing the second card, the
probability is 1/4 x 1/4 =1/16 This is the same as 1/4 x 1/4 = 1/16.Or
we can consider experiment as picking two cards at a time. For each of
them probability to turn out spade is 1/4. On the other hand, if we
draw firstly one card& it is spade with probability 1/4. If a second
card drawn, there's one less spade in the deck, so the probability on
the second draw is 12/51. The probability of drawing two spades from a
deck is 0.25 x 12/51 = 0.058824 This is called sampling without
replacement. In quality control, it is very common to sample without
replacement as bad parts are discarded.
Neil Schliewe
03.04.12, 15:12
Don't you have to account for the fact that this is a dependent event?
Taking 2 cards the second card should be only 12/51 - correct?
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In fact this question is a little bit tricky. If we consider drawing one card, putting it back in the deck, regardless if it is a spade or not, then reshuffling the deck and drawing the second card, the probability is 1/4 x 1/4 =1/16 This is the same as 1/4 x 1/4 = 1/16.Or we can consider experiment as picking two cards at a time. For each of them probability to turn out spade is 1/4. On the other hand, if we draw firstly one card& it is spade with probability 1/4. If a second card drawn, there's one less spade in the deck, so the probability on the second draw is 12/51. The probability of drawing two spades from a deck is 0.25 x 12/51 = 0.058824 This is called sampling without replacement. In quality control, it is very common to sample without replacement as bad parts are discarded.
Don't you have to account for the fact that this is a dependent event? Taking 2 cards the second card should be only 12/51 - correct?
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