Probability

2007-04-04 3:12 am

12 cards, 8 are each marked with a square and 4 are marked with circle.A card is drawn and replaced.Another card is then drawn at random.if totally 3 cards are drawn ,what is the probability of getting two cards with squares and a card with a circle?

回答 (3)

little minnie

2007-04-04 4:48 am

✔ 最佳答案

the prob. of square card is 8/12,
and the prob. of circle card is 4/12

if 3 cards are drawn, and we want the prob. of (2 square and 1 circle),
the sample space are: ( 1st is square, 2nd is square, 3rd is circle) or
( 1st is square, 2nd is circle, 3rd is square) or
( 1st is circle, 2nd is square, 3rd is square)
= (8/12*8/12*4/12) + (8/12*4/12*8/12) + (4/12*8/12*8/12)
= (8/12*8/12*4/12) x 3
= 12/27 or 0.44444

siminarly,
if 3 cards are drawn, and we want the prob. of (2 circle and 1 square),
the sample space are: ( 1st is square, 2nd is circle, 3rd is circle) or
( 1st is circle, 2nd is square, 3rd is circle) or
( 1st is circle, 2nd is circle, 3rd is square)
= (8/12*4/12*4/12) + (4/12*8/12*4/12) + (4/12*4/12*8/12)
= (8/12*4/12*4/12) x 3
= 2/9 or 0.22222

參考: my maths. knowledge

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yy yy

2007-04-04 3:35 am

4/12*4/12+4/12*4/12+8/12*8/12
=2/3

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Cecilia

2007-04-04 3:34 am

P(2 squares and a circle)
=( 4/12 x 4/12 x 8/12 ) x 3
=4/9

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