Question

The population of a type of local frog can be found using an infinite geometric series where a one equals 84 and the common ratio is one over five find the sum of the infinite series that will be the upper limit of this population. 87,105,425, or this series is divergent

Answer 1

A=84 and r=1/5

Since r, the common ratio squared is less than one, the sum will converge to a limit.  Rule:  if  r^2<1 infinite series converges, otherwise it diverges.

Since the sum of any geometric sequence is:

s(n)=a(1-r^n)/(1-r)

And if r^2<1, (1-r^n) becomes 1-0=1 as n approaches infinity.

So whenever r^2<1 the sum of the infinite series is just:

s(n)=a/(1-r)

Since a=84 and r=1/5 this infinite series has a sum of:

s(n)=84/(1-1/5)

s(n)=84/(4/5)

s(n)=5(84)/4

s(n)=105