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

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In a sequence of terms in which each term is three times the [#permalink]

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30 Oct 2006, 06:37
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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.
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30 Oct 2006, 07:35
))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
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30 Oct 2006, 07:57
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.
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30 Oct 2006, 23:27
only A.

2 is not suff, because the first could be 3, or 9, or 27 etc.
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30 Oct 2006, 23:40
Yurik79 wrote:
Priyah wrote:
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.

Oops you are right))it is 81

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

(A)
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31 Oct 2006, 02:30
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
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31 Oct 2006, 04:19
this is a GP(geometric progression)

A stands
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31 Oct 2006, 11:04
Code:
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?
31 Oct 2006, 11:04
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