一條f.5 maths probability mc問題(15points) URGENT!

[匿名]

2008-04-02 2:13 am

A box contains 10 calculators of which 3 are faulty. 3 calculators are picked at random without replacement and checked one by one. What is the probability that there are 2 faulty ones in the sample, given that the first one is not faulty?
A. 7/120
B. 7/40
C. 5/12
D. 1/12

Ans. A

Can u plz explain it briefly? thz a lot

回答 (1)

用戶28531

2008-04-02 2:19 am

✔ 最佳答案

一條f.5 maths probability mc問題(15points) URGENT!

A box contains 10 calculators of which 3 are faulty. 3 calculators are picked at random without replacement and checked one by one. What is the probability that there are 2 faulty ones in the sample, given that the first one is not faulty?
A. 7/120
B. 7/40
C. 5/12
D. 1/12

Ans. A

Can u plz explain it briefly? thz a lot

>>>>> Steps
1st Calculator picked (GOOD) : 7 / 10
2nd calculator picked (faulty) : 3 / 9
3rd calculator picked (faulty) : 2 / 8
( 7/10 ) ( 3/9 ) ( 2/8 ) = 7/120

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