Question

The total number of fungal spores can be found using an infinite geometric series where a1 = 9 and the common ratio is 5. Find the sum of this infinite series that will be the upper limit of the fungal spores.
Select one:
a. 95
b. The series is divergent.
c. 80
d. 25

Answer 1

now if the common ratio is 5
then the series looks like
9 , 45 , 225..
correct ?

Answer 2

Yes i believe so, either that or adding 5 to the next

Answer 3

they said
"geometric series"
it means that we multiply
and also we talk about common ratio (another hint for the multiplication)

Answer 4

Okay, then yes correct

Answer 5

so for a geometric series with common ratio r such that
|r| > 1
(absolute value)
the series will diverge

and i guess you can see it using your intuition - the numbers are always getting larger
and we keep adding them

Answer 6

but i'm not sure how to get a sum because it doesn't say where the series stops

Answer 7

the last thing i said was only for infinite geometric series like we have

Answer 8

Okay so the series will be divergent?

Answer 9

yes

Answer 10

if however |r| < 1
we can find the sum.

Answer 11

uhhh okay i think i understand, thank you

Answer 12

yw

Answer 13

So basically it is divergent, hence the wording of the question "infinite series"