about probability(urgent!!!10)

2010-12-08 5:22 am

The programmes offered by a community college are open to all enrollments without any special entrance requirement. Past records indicate that 7 out of 10 of the participants would drop out before completing the enrolled programmes.Twenty participants are randomly selected from the list of all enrolled participants.What is the probability that :
(a)exactly 5 out of these 20 participants would complete their enrolled programmes in the college?
(b)10 or more of these 20 paricipants would complete their enrolled programmes in the college?
(show all workings and correct to 3 decimal places in your answers.)

回答 (1)

Acct

2010-12-09 2:31 am

✔ 最佳答案

(a) Combination: nCr = 20C5 = 15504
P(complete) = 3/10
P(incomplete) = 7/10

(3/10)^5 x (7/10)^15 x nCr
=0.00243 x 0.004747561 x 15504
=0.1789

(b) Combination: nCr = 20C10 184756
=(3/10)^10 x (7/10)^10 x nCr
=0.0308

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