Answer:
18.
Step-by-step explanation:
It is a geometric sequence.
The common ration is 1/3.
The nth term of a GS is a1 r(n-1)
The first term of this GS is 645700815.
Substituting to see which term is 5:
Try 16:
16th term = 645700815 * (1/3)^(16-1)
= 45
18th term = 645700815 * (1/3)^(18-1)
= 5.
So there are 18 terms.
