SOLUTION: A computer is infected with a virus, assume that it infects 20 other computers within 5 minutes, and that these pc's and servers each infect 20 more machines within another 5minute

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Question 117057: A computer is infected with a virus, assume that it infects 20 other computers within 5 minutes, and that these pc's and servers each infect 20 more machines within another 5minutes, etc. How long until 100million computers are infected
Answer by edjones(8007) About Me  (Show Source):
You can put this solution on YOUR website!
The is a geometric sequence.
S(n)=a(1)((1-r^n)/(1-r)) sum of a finite geometric sequence.
Since a(1)=1 we can leave it out without changing the result.
r=20
When n=7.131853 by my TI-89 calculator S(n)=100,000,000
7.13*5=35.65
So, by 36 minutes 100,000,000 computers are infected.
.
Ed