Given: There are 7 billion, that is, 7*10^9

people on Earth. If a bird flu virus starts

with one person and within 5 days two

people are infected, then each of those two

people in 5 days infects 2 people each,

and so on, how many days before everyone

on earth is infected?

Hint: Geometric series and logarithms

I know this formula....N(t)= 1e(rt) but what would the rate (r) be?

how do i do this??