There are 120 ping-pong balls in a basket.20 of the balls cannot bounce well,15 have wrong company logos and 5 have both defects.
(b)If two balls are selected one by one at random with replacement,what are the probabilities that
(i)exactly one of the balls is fefective?
(ii)both of them are defective?
probability
2011-12-29 1:37 am
回答 (2)
2011-12-29 1:47 am
✔ 最佳答案
There are 20 + 15 - 5 = 30 ping-pong balls which have defects(b)(i) P(exactly one of the balls is defective)
= (30/120)(90/120) + (90/120)(30/120)
= 3/8
(ii) P(both of them are defective)
= (30/120)(30/120)
= 1/16
2011-12-29 2:07 am
total no. of defective balls : 20 + 15 + 5 = 40
(i) 40/120 x 80/120 x 2
= 1/3 x 2/3 x 2
= 4/9
(ii) 40/120 x 40/120
= 1/3 x 1/3
= 1/9
(i) 40/120 x 80/120 x 2
= 1/3 x 2/3 x 2
= 4/9
(ii) 40/120 x 40/120
= 1/3 x 1/3
= 1/9
收錄日期: 2021-04-26 19:18:17
原文連結 [永久失效]:
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