Forever Six

Algebra Level 2

1 6 + 1 6 2 + 1 6 3 + 1 6 4 + . . . = ? \frac{1}{\color{#69047E} 6} + \frac{1}{\color{#69047E} 6^{2}} + \frac{1}{\color{#69047E} 6^{3}} + \frac{1}{\color{#69047E} 6^{4}} + ... = \ ?

0.2 0.1 0.25 0.15

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12 solutions

Mohammad Al Ali
May 19, 2014

Restating the equation required,

x = 1 6 + 1 6 2 + 1 6 3 + + 1 6 4 + . . . x = \frac{1}{6} + \frac{1}{6^{2}} + \frac{1}{6^{3}} + + \frac{1}{6^{4}} + ...

Multiplying both sides by 6 we obtain,

6 x = 1 + 1 6 + 1 6 2 + 1 6 3 + 1 6 4 + . . . 6x = 1 + \frac{1}{6} + \frac{1}{6^{2}} + \frac{1}{6^{3}} + \frac{1}{6^{4}} + ...

Notice that the RHS is equivalent to 1 + x 1+x , which can be written as

6 x = 1 + x 6x = 1 + x

Solving for x x , x = 1 5 = 0.2 \boxed{ x = \frac{1}{5} = 0.2}

excellent explanation

Umang Vasani - 7 years ago

Questions dealing with Infinity are just too exciting...................

Sourabh shukla - 6 years, 10 months ago

excellent ....................

Bazmi Farooquee - 6 years, 10 months ago

* absolutely Brilliant *

Praneeth Reddy - 6 years, 9 months ago

Yes, I got the answer the same way. X = 0.2 Ans K.K.GARG,India

Krishna Garg - 7 years ago

Beautiful.

Bernardo Sulzbach - 6 years, 11 months ago

You put the plus sign twice there between 1/6^3and1/6^4

Abdur Rehman Zahid - 6 years, 8 months ago

I just divided x by 6 otherwise the answer was the same!!!

Abdur Rehman Zahid - 6 years, 8 months ago
Basukinath Tiwari
May 19, 2014

This is a simple GP question and the formula to find sum of infinite terms is =A/(1-R) where A is the first term and R is the ratio of first and second terms basically second term / first term.

Hassan Raza
Jul 31, 2014

L e t S = 1 6 + 1 6 2 + 1 6 3 + 1 6 4 + . . . . . . . . . . . . . . . . . . . . . M u l t i p l y i n g B o t h s i d e s b y " 6 " , w e h a v e 6 S = 1 + 1 6 + 1 6 2 + 1 6 3 + 1 6 4 + . . . . . . . . . . . . . . . . . . . . . = > 6 S = 1 + S = > 6 S S = 1 = > 5 S = 1 o r S = 1 5 T H u s t h e a n s w e r i s S = 0.2 Let\\ \qquad S=\frac { 1 }{ 6 } +\frac { 1 }{ { 6 }^{ 2 } } +\frac { 1 }{ { 6 }^{ 3 } } +\frac { 1 }{ { 6 }^{ 4 } } +.....................\infty \\ Multiplying\quad Both\quad sides\quad by\quad "6",\quad we\quad have\\ \qquad 6S=1+\frac { 1 }{ 6 } +\frac { 1 }{ { 6 }^{ 2 } } +\frac { 1 }{ { 6 }^{ 3 } } +\frac { 1 }{ { 6 }^{ 4 } } +.....................\infty \\ =>6S=1+S\\ =>6S-S=1\quad =>\quad 5S=1\\ or\quad S=\frac { 1 }{ 5 } \\ THus\quad the\quad answer\quad is\quad \boxed { S=0.2 }

Brilliantly Explained...

Rhyth Mehta - 5 years, 10 months ago
Tony Kappen
Feb 3, 2017

Let 1 6 + 1 6 2 . . . = x \frac {1}{6} +\frac {1}{6^2} ... = x . Then factor out the 1 6 \frac {1}{6} from the second term onwards. Thus you end up with 1 6 + 1 6 ( 1 6 + 1 6 2 + . . . ) = x \frac {1}{6} + \frac {1}{6}(\frac {1}{6} +\frac{1}{6^2}+...) = x . Remember that you set the expression in the brackets as x. Thus you substitute x in for the expression in the brackets. You will end up with 1 6 + 1 6 x = x \frac {1}{6} +\frac {1}{6}x = x . Solve for x and you will get 0.2.

Aminu Abdullahi
Feb 9, 2015

By using sum of Geometric series formula S= a(1- r^n/1-r) where a= 1/6 , common ratio r= 1/6 and n= 4 the answer is 0.2

Yajnaseni Jena
Feb 8, 2015

thanks for question

Ibraheem Akram
Feb 6, 2015

S=a/1-r
a=1/6 & r=1/6
so
S=1/5=0.2


Navnith H Nath
Feb 5, 2015

Equation for infinite GP , S=a/(1-r). So, S=(1/6)/(1-(1/6))=0.2

Oli Hohman
Feb 4, 2015

Geometric series with a1 = 1/6 and r = 1/6

Sum = a1/(1-r)

= (1/6)/(1-1/6) = (1/6)/ (5/6) = 1/5 = .2

Pankaj Nirwan
Jul 16, 2014

S = a/1 - r

so a =1/6 , b = 1/36 and r = b/a =1/36 /1/6 = we get r = 1/6 so , put the value of a , r in above formula S = 1/6 /1- 1/6 = 1/5 = 0 .2

Deepak Gowda
Jun 20, 2014

infinite sum = a / 1- r, where a is first term and r is common ratio.

here a = 1/6 = r

infinite sum = (1 /6 ) / (1 - (1 / 6) ) = 1/ 5 = 0.2

Karishma Jain
Jun 4, 2014

lets add 1and subtract 1 then, 1+1/6+1/6square+.....-1 now using infinite gp 1/(1-1/6) -1 6/5-1 1/5 0.2

I used the Euler's form to solve this eqn.

Ariijit Dey - 6 years, 11 months ago

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