In a sequence of terms in which each term is three times the

Question

In a sequence of terms in which each term is three times the previous term, what is the fourth term?

(1) The first term is 3.

(2) The second to last term is 3^10.

Yurik79 · Answer

))tricky question
IMHO A it is
1) is obvious 
1st term is 1 
second=3
third=9
and fourth =27
2)tricky The second to last term is 3^10.
insuff since we don't know how many terms there are in the sequence

Priyah · Answer

This Seq is defined by 
S={ n, 3n, 3^2 n. 3^3 n.....

From S1, n=3, so 4th term will be 81.
From S2, second last term is 3^10...but,since total nbr of terms in seq not given, we cannot say which is the 4th term.

Hence A.

tennis1ball · Answer

only A.

2 is not suff, because the first could be 3, or 9, or 27 etc.

GMATT73 · Answer

Good catch Yurik. Yes, for statement (2) we don't know the total number of terms..

(A)

ugo_castelo · Answer

You're right

must be A

for B, if first term n=1 then i(nb of terms)= 12 since the value of last term is determined by: n*3^(i-1)
if n=3 then i=11
so we cannot determin the 4th term value

trivikram · Answer

this is a GP(geometric progression)

A stands

girikorat · Answer

this is a GP(geometric progression) 
 

Trivikram,
Can you post the formulae for GP??

Like what we have for AP - the last term, Sum of n terms etc...
What formulae do we have for GP?

Also, HP is just the sum of reciprocal of terms in an AP.
Do we have formulae for that as well?

In a sequence of terms in which each term is three times the

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards