The population of a local species of flies can be found using an infinite geometric series where a1 = 940 and the common ratio is one fifth. Write the sum in sigma notation, and calculate the sum (if possible) that will be the upper limit of this population.

Respuesta :



A geometric series is the sum of the terms of a geometric sequence of  the form [tex]a, ar, ar^{2}, ar^{3},... [/tex], 
where r is the common ratio, and a≠0 is the first term.

That is, the series is  [tex]a+ar+ar^{2}+ar^{3},... [/tex]

In sigma notation, the series is written as:


∑  [tex]a r^{k} [/tex] 
k=0
--------------------------------------------------------------------------------------------------

The geometric series of the form

∑  [tex]a r^{k} [/tex], converges to [tex] \frac{a}{1-r} [/tex] if |r|<1
k=0

and diverges otherwise.
--------------------------------------------------------------------------------------------------

in our problem, a , the first term is equal to 940, and the common ratio is |1/5|<1, 

thus the series converges to:
[tex] \frac{a}{1-r}=\frac{940}{1-1/5}=\frac{940}{4/5}=752[/tex]


Answer: 

∞          
∑  [tex]940 (1/5)^{k} [/tex]=752   ( the upper limit of the population is 752)
k=0