Verbal Reasoning - Series Completion - Discussion

Choose the correct alternative that will continue the same pattern and replace the question mark in the given series.

4. 

In the series 2, 6, 18, 54, ...... what will be the 8th term ?

[A]. 4370
[B]. 4374
[C]. 7443
[D]. 7434

Answer: Option B

Explanation:

Clearly, 2 x 3 = 6, 6 x 3 = 18, 18 x 3 = 54,.....

So, the series is a G.P. in which a = 2, r = 3.

Therefore 8th term = ar8-1 = ar7 = 2 x 37 = (2 x 2187) = 4374.


Prem said: (Jul 18, 2011)  
We have to go with formula only ?

Aman said: (Jul 24, 2011)  
Not understandable.

Kanna said: (Aug 16, 2011)  
If we don't know formula we can go in simple logic

2,6,18,54,5th term,6th term,7th term,8th term(here we should get answeer)
So

2 x 3 = 6,
6 x 3 = 18,
18 x 3 = 54,
54 x 3=162(5th term),
162 x 3=486(6th term),
486 x 3=1458(7th term),
1458 x 3=4374(8th term and our answer)

Appy said: (Aug 19, 2012)  
How do we find 3^7 without using " calculator and multiplying 3 seven times " ? please tell me the easy method to find out a number raised to a large power.

Bhumika said: (Sep 9, 2012)  
I dont understand the answer.2,6,18,54,5th term,6th term,7th term,8th term(here we should get answeer) .how it comes 4374

Aswini said: (Oct 14, 2012)  
What does GP mean?can anyone explain me please.

Avinash Wadhe said: (Nov 22, 2012)  
GP means Geometric Progression formula.

Sahiba said: (May 23, 2013)  
Geometric progression is one where a set of numbers vary with one number which is multiplied to each one to get the next term.

Ex:2(2*3) = 6(6*3) = 18....

So now 2 6 18... are in gp differing by 3 each.

Arif said: (Jun 28, 2013)  
There should be some easy method to solve this, Can any one have?

Biji said: (Aug 1, 2013)  
A = 2.
R = 3.
N = 8 th term.
= 2*3^(8-1).
= 2*3^7.
= 2(3^7) = 2(3^2 * 3^2 * 3^2 * 3).
= 2(9*9*9*3) = 2(81*27).
= 2(2187) = 4374.

3^7 = 3 square * 3 Square * 3 Square * 3.

Sameer said: (Nov 7, 2013)  
@Kanna.

Why we need to multiply with 3 With Given Numbers?

Manjot Singh said: (Mar 1, 2014)  
2*3 = 6.
6*3 = 18.
18*3 = 54.
54*3 = 162.
162*3 = 486.
486*3 = 1458.
1458*3 = 4374.

Sangeeta said: (Nov 26, 2014)  
This series is in geometric progression:

So 8th term is = 2*3^(8-1).

= 2*3^(7).
= 2*3^(4+3).
= 2*[3^4*3^3].
= 2*[81*27].
= 2*2187.
= 4374.

Chiran said: (Feb 8, 2015)  
What is the meaning of a and r please explain me?

Kanhay said: (Feb 8, 2015)  
A means first term and are means common ratio.

Upender Singh Rajput said: (Jul 19, 2015)  
Solving with GP. (Geometrical Progression) find 8th term.

Now Series is 2 6 18 54.....8th term.

So a =2, r=6\2=3, T8=2(3)7, T8 = 4374.

Nrusingha Acharya said: (Jan 21, 2016)  
An other method: 2.

6*3^0.
6*3^1.
6*3^2.
6*3^3.
6*3^4.
6*3^5.
6*3^6,

Only calculate the 8th one not all and get the result.

Sameer said: (Jan 26, 2016)  
Why ^7 instead ^8 because there find out 8th place?

Nigerian Boy said: (Feb 22, 2016)  
@Sameer.

From the formula T8 = ar (power N-1).

N stands for Number of terms you are looking for so all you need do is know that you have to subtract 1 from the number of terms.

Eg. 1. When the number of terms in question is 9 then the formula becomes T9 = ar9-1.

2. When it is 5 the formula becomes T5 = ar5-1.

Vaishnavi said: (May 21, 2016)  
Yes, using formula is also the correct method.

Amrit Hayer said: (Aug 11, 2016)  
The sum of first 3 terms of G.P is 16 and the sum of next 3 terms is 128. Find 1st term, common ratio and sum 20 terms? please solve this.

Madalin said: (Jul 13, 2021)  
2 + 2 = 4 + 2 = 6,
6 + 6 = 12 + 6 = 18,
18 + 18 = 36 + 18 = 54,
54 + 54 = 108 + 54 = 162,
162 + 162 = 324 + 162 = 486,
486 + 486 = 972 + 486 = 1458,
1458 + 1458 = 2916 + 1458 = 4374.

2, 6, 18, 54, 162, 486, 1458, 4374. 8th term is 4374.

Papai said: (Aug 9, 2021)  
ar^n-1 where n=no of term, a=first elementary.
So,
2*3^7=4374.

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