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virus merges

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by sanju09 » Tue Feb 16, 2010 5:55 am
Direction: There is a peculiar species of virus in which one virus merges with another to give a single virus. One virus can merge with only one in a particular day. However, if fails to find another one in the day, it dies. Also, the viruses can find each other wherever they are.

If there are 2 n - 1 virus, then after how many days will all of them die?

(A) 2 n - 1
(B) n + 1
(C) n
(D) n - 1
(E) 2 n

[spoiler]source: www.topgmatcoaching.com

This site has shown so many ambiguous questions but this one seems OK. I don't have the OA.[/spoiler]
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by ajith » Tue Feb 16, 2010 6:25 am
sanju09 wrote:Direction: There is a peculiar species of virus in which one virus merges with another to give a single virus. One virus can merge with only one in a particular day. However, if fails to find another one in the day, it dies. Also, the viruses can find each other wherever they are.

If there are 2 n - 1 virus, then after how many days will all of them die?

(A) 2 n - 1
(B) n + 1
(C) n
(D) n - 1
(E) 2 n

[spoiler]source: www.topgmatcoaching.com

This site has shown so many ambiguous questions but this one seems OK. I don't have the OA.[/spoiler]
Is it 2^n -1 or 2*n-1

Please confirm!
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by sanju09 » Tue Feb 16, 2010 6:36 am
Again! It's 2 n - 1.
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by ajith » Tue Feb 16, 2010 6:42 am
sanju09 wrote:Again! It's 2 n - 1.
say n =22

there were 45 viruses (2n-1 = 2*22-1 = 45)

first day make 22 pairs on that day and 1 dies

second day they make 11 pairs and none dies

third day they make 5 pairs and 1 dies

fourth day they make 2 pairs and 1 dies

fifth day they make 1 pair and none dies

sixth day the remaining one dies

now the no of days is =6 and n = 22

A, B, C, D , E ruled out and it's a nonsensical question

Wherein if it is 2^n - (1) it would have made sense, alas!
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