top button
Flag Notify
    Connect to us
      Facebook Login
      Site Registration

Facebook Login
Site Registration

Which term of the Geometric Progression 5,10,20,40...is 5120?

0 votes
652 views
Which term of the Geometric Progression 5,10,20,40...is 5120?
posted Oct 28, 2016 by anonymous

Share this puzzle
Facebook Share Button Twitter Share Button LinkedIn Share Button

4 Answers

0 votes

11th

5
10
20
40
80
160
320
640
1280
2560
5120

answer Oct 28, 2016 by Salil Agrawal
0 votes

From geometric progression,

Gn =G_1 r^(n-1).............................1

but
Gn = 5120
G1 = 5
r = 10÷5
=2

5120 = 5 * 2^(n-1)

2^(n-1) = 5120\5
= 1024
= 2^(10)

i.e.
n - 1 = 10

so
n = 11

so it is 11th term.

answer Oct 28, 2016 by Justine Mtafungwa
0 votes

Given the geometric progression:
a 1 = 5
a 2 = 5 x 2 = 10
a 3 = 10 x 2 = 20 or a 1 x 2^2 = 5 x 4 = 20
Then, we can write:
a n = a1 x 2 ^(n - 1) being n the term of the progression
Then,
an = 5120 = 5 x 2 ^(n-1)
Solving this equation
For n= 11 , 2 ^10 = 1024 , 1024 x 5 = 5120
The term is n= 11

answer Nov 6, 2016 by anonymous
0 votes

Clearly:
The common ration = 10 / 5 = 2.
therefore, a = 5; r = 2;
As, we know,

a*r^n-1=5120
:5*2^n-1 = 5120
:2^n-1 = 1024
:2^n-1 = 2^ 10
: n - 1= 10
n = 11

answer Apr 8, 2017 by Nabhonil Jana



Similar Puzzles
0 votes

First and last term of a geometric progression are 3 and 96. If the sum of all these terms is 189, then find the number of terms in this progression.

0 votes

The sum of the first three terms of a geometric progression is 8. The sum of the first six terms of the same geometric progression is 12.

Find the common ratio of this geometric progression?

Contact Us
+91 9880187415
sales@queryhome.net
support@queryhome.net
#280, 3rd floor, 5th Main
6th Sector, HSR Layout
Bangalore-560102
Karnataka INDIA.
QUERY HOME
...