Answer:
D. 5
Explanation:
a geometric sequence is defined that any item of the sequence is created by multiplying the previous item of the sequence with a constant factor (it is the same factor for every item in the sequence).
so, we have the starting value
a1 = 3
then
a2 = 15
what is a multiplication factor to go from 3 to 15 ?
well, 5. I need to multiply a1 by 5 to get a2.
and this continues.
a3 = a2×5 = 15×5 = 75
a4 = a3×5 = 75×5 = 375
and so on.
the ratio of the sequence is simply the relation of one sequence item to the previous one :
an/an-1
and that is here for the described reasons 5.