SOLUTION: This is one of the questions in a test that I wasn't able to answer. In the geometric sequence, a-sub1 = 1 and a-sub4 = 27, find a-sub7. A. 2992 B. 1953 C. 2187 D. 211

Question 836400: This is one of the questions in a test that I wasn't able to answer.
In the geometric sequence, a-sub1 = 1 and a-sub4 = 27, find a-sub7.
A. 2992
B. 1953
C. 2187
D. 2110

Thanks,
Shayne
Found 2 solutions by Alan3354, KMST:
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
Hint: 27 = 3^3

Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!

In a geometric sequence,
= common ratio
for any natural number

so
(You must know that so you know where I got that value).

You see that choices A and D are not even multiples of 3, so they are not the answer.
(If they were multiples of 3, their digits would add up to 3, 6, 9, or some other multiple of 3).

I see immediately that B and C are also wrong, because the answer should be between 625 and 900:
<-->
It may be a typo (not necessarily your fault), or else someone is making a mistake in the calculations (and I say not me).
However,
and
I would choose answer
and use judgement about confronting the teacher, or textbook maker about their mistake. If you already had the test, make sure you did not misread the question, and if the question was wrong, meekly point out that you knew the right answer, but were confused and frustrated by the choices given. Maybe you can gain more points that way.
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