Applications of Bases: Part I, Problem 1

Jason is listing out all numbers which have only the digits 0 and 1 in order. He begins writing the sequence: 1 , 10 , 11 , 1, 10, 11, \ldots What position is the number 101101 in this sequence?

If you liked this problem, check out the other problem in Application of Bases set.


The answer is 45.

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9 solutions

Matthew Lipman
Mar 21, 2014

We note that the nth number is just n in binary! Therefore, 101101 is the 101101(base 2)th number. 101101(base 2)=45, so we conclude that it is the 45th number in the list.

The given answer is not a number theory problem. If the question is considered as a number theory problem, its answer would be 63653. It means 101101 would be on 63653rd position.

E.g. 1,10,11,12,13...19,20,21,30,31,40,41,50,....91,100,101,102........101101 P.S.- This problem is not framed properly.

Kamal Sharma - 7 years, 2 months ago

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Wait. It said that the person only list numbers with 0 or 1 only. So, yeah, your reasoning is wrong.

Joeie Christian Santana - 7 years, 2 months ago

Good thing to know :

1 0 1 1 0 1 32 + 0 16 + 8 +4 + 0 2 +1 = 45

Pablo Moran - 7 years, 2 months ago

binary number convert into decimal number ..

Sarang Deshmukh - 7 years, 2 months ago

good

Qamar Raj - 7 years, 2 months ago

piece of cake, just convert binary into decimal...!

Minhaj Hussain - 7 years, 2 months ago
Tunk-Fey Ariawan
Mar 31, 2014

The series will form the first n n -term of binary sequence and the position of 101101 101101 is the sequence of n n -term in decimal number. Therefore, to determine the position of 10110 1 2 101101_2 all we have to do is just converting 10110 1 2 101101_2 to base 10 10 . 10110 1 2 = ( 1 × 2 5 + 0 × 2 4 + 1 × 2 3 + 1 × 2 2 + 0 × 2 1 + 1 × 2 0 ) 10 = 45 \color{#D61F06}{101101_2}=(\color{#D61F06}{1}\times2^5+\color{#D61F06}{0}\times2^4+\color{#D61F06}{1}\times2^3+\color{#D61F06}{1}\times2^2+\color{#D61F06}{0}\times2^1+\color{#D61F06}{1}\times2^0)_{10}=\boxed{\color{#3D99F6}{45}}


# Q . E . D . # \Large\color{#3D99F6}{\text{\# }\mathbb{Q.E.D.}\text{ \#}}

well solved...

Akshay Mishra - 7 years, 2 months ago

i liked it........... :D

Max B - 7 years, 2 months ago
Uahbid Dey
Mar 31, 2014

( 101101 ) 2 = ( 1 × 2 5 ) + ( 0 × 2 4 ) + ( 1 × 2 3 ) + ( 1 × 2 2 ) + ( 0 × 2 1 ) + ( 1 × 2 0 ) \left ( 101101\right )_{2}=\left ( 1\times 2^{5} \right )+\left ( 0\times 2^{4} \right )+\left ( 1\times 2^{3} \right )+\left ( 1\times 2^{2} \right )+\left (0\times 2^{1} \right )+\left ( 1\times 2^{0} \right ) = 32 + 0 + 8 + 4 + 0 + 1 = 45 =32+0+8+4+0+1=45

gud

Viswakanth Kandala - 7 years, 2 months ago

2^5 + 0 + 2^3 + 2^2 + 0 + 2^0 = 45 Uhm binary digits

Amogh Jain
Mar 30, 2014

101101(2)=45(10)

here nth no# is in binary no#...means base 2 so there decimal value identity it's place value or say position in chronological order of 0 and 1

It is not a number theory question , it is a computer science.

Raven Herd - 7 years, 2 months ago

Hello all,

as the binary series mentined as 1,10,11............,101101....., what is the the position 101101?

change those to decimals,

1,10,11......=1,2,3......,45....,i make them as an arithmetic series,

as for 1011011 = 45,

a=1, d=1, Tn=45,

Tn = a+(n-1)d

45 = 1+ (n-1)1

45 =1 + n -1

n=45,

Therefore, 101101 it is in 45th position in the series.....

1-1 10-2 11-3......................... 101101-45 here, sequence starts at 1 in 1st position and continued with a common difference of 1 up to 45. therefore, number position 1 1 10(2) 2 11(3) 3 .. .. 101101(45) 45

DaNyal Al-lmed
Mar 31, 2014

This question is as simple as tricky it looks if you have a sharp mind that can quickly get to work to the problem than you have no problem to solving it Using conversion of binary to decimal 101101=1x2^5+0x2^4+1x2^3+1x2^2+0x2^1+1x2^0=45 :P

Hell.......this question does not related with binary system .........considering with airthmatic means

Harinder pal - 7 years, 1 month ago

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