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# 15 computers in the computer network are infected with

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Manager
Joined: 24 Jun 2006
Posts: 62
Followers: 1

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15 computers in the computer network are infected with [#permalink]  16 Sep 2006, 13:55
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15 computers in the computer network are infected with virus. If every day several computers are arbitraril selected for scanning, what is the probability that no computer containing virus will be scanned in the next 5 days.

1) 10 computers are scanned everyday
2) 4% of all computers are scanned everyday.

(Note - Please let me know the probability if the above problem was a Quant Problem and it was already given that there are 250 computers in the lab.)

Thanks,

Mitul
Senior Manager
Joined: 20 Feb 2006
Posts: 373
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Kudos [?]: 7 [0], given: 0

I'm going with C

15 computers in the computer network are infected with virus. If every day several computers are arbitraril selected for scanning, what is the probability that no computer containing virus will be scanned in the next 5 days.

1) 10 computers are scanned everyday
2) 4% of all computers are scanned everyday.

From 1) We cannot calculate a probability because we do not know an absolute no of values and therefore cant calculater no. of favourable outcomes/no. of outcomes INSUFF

From 2) We dont know absolute no of computers or number that 4% represents. INSUFF

From 1&2 - We can work out absolute no of computers 10*100/4 and so can then calculate probability.

I'll try and post the probability using the binomial but you may have to wait til the morn (is nearly 2am in UK now)
Intern
Joined: 26 Jun 2006
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I select C

As from (1) and (2), I can get the total number of computer.
4% of X = 10
X = 250

Prob. of select computer that not infect for one day = (250-15) / 250
= 235/250
Prob. of select computer that not infect for 5 day = (235/250)^5
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