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A box contains 5 black and 4 white balls. If two balls are drawn at random, what is the probability that one is white and the other is black?

2007-04-12 19:06:24 · 4 answers · asked by Anonymous in Science & Mathematics Mathematics

4 answers

If the first ball is replaced
P = (5/9)(4/9) = 20/81

If the first ball is not replaced
P = (5/9)(4/8) + (4/9)(5/8) = 40/72 = 5/9

2007-04-12 19:16:50 · answer #1 · answered by Helmut 7 · 0 0

P = 4/9 * 5/8 = 20/72 = 0.27778

4/9 is the probability of 1 white ball being picked up from the lot (9 balls = 5 + 4)
5/8 is the probability of a black ball (9 - 1the first picked ball)

2007-04-12 20:00:47 · answer #2 · answered by Anonymous · 0 0

Without replacement
P(one of each) = P(WgB)*P(B) + P(BgW)*P(W)
where WgB means white given black
P(one of each) = (4/8)*(5/9) + (5/8)*(4/9) = 40/72 = 5/9

2007-04-12 19:22:58 · answer #3 · answered by Anonymous · 0 0

5C1 / 9C1 x 4C1 / 8C1
5/9 x 1/2 = 2.5/9 = .277777

2007-04-12 19:13:54 · answer #4 · answered by rakham22 1 · 0 1

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