Verbal Reasoning - Series Completion - Discussion
Discussion Forum : Series Completion - Section 1 (Q.No. 4)
Directions to Solve
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 ?
Answer: Option
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.
Discussion:
27 comments Page 1 of 3.
Nigerian boy said:
10 years ago
@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.
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.
(1)
Kanna said:
1 decade ago
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)
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)
Madalin said:
4 years ago
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.
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.
(15)
Sahiba said:
1 decade ago
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.
Ex:2(2*3) = 6(6*3) = 18....
So now 2 6 18... are in gp differing by 3 each.
Biji said:
1 decade ago
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.
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.
Appy said:
1 decade ago
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.
Sangeeta said:
1 decade ago
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.
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.
Upender Singh Rajput said:
1 decade ago
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.
Now Series is 2 6 18 54.....8th term.
So a =2, r=6\2=3, T8=2(3)7, T8 = 4374.
Amrit hayer said:
9 years ago
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.
(1)
Nrusingha acharya said:
10 years ago
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.
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.
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