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What is the smallest positive value of N N , such that there exists (not necessarily positive) integers x x and y y satisfying

2013 x + 3102 y = N ? 2013 x + 3102y = N ?


The answer is 33.

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11 solutions

Jit Ganguly
Nov 24, 2013

See guys, looking at it you can see that it's a linear Diophantine equation in 2 variables. of the form a x + b y = N ax+by=N . Now suppose g c d ( a , b ) = d gcd( a, b)=d ,where a , b , x , y , d a,b,x,y,d are integers .Now for the existence of a solution ,as d d divides a x + b y ax+by ..........so in turn, d must divide N.
( Well this is because if g c d ( a , b ) = d gcd(a,b)=d , then d divides both a and b, so d divides a x + b y ax+by for integers x , y x,y )

So, in order for the existence of solution of the given equation, g c d ( 2013 , 3102 ) = 33 gcd(2013,3102)=33 must divide N N . So 33 must divide N,i.e N must be a multiple of 33. Clearly the smallest such N is 33 . Well this is my first time I wrote a solution and also that using the code, so sorry for the disalignment in writing.

Ok so if N is 33, what are the values of x and y then? I was able to factorise the equation to get ,

33(61x+94y)=N

but how exactly do u prove N=33 ?

The Math Slayer - 7 years, 6 months ago

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61 and 94 are relatively prime, so there exist x and y such that 64x+91y=1=N/33. Since 1 is the smallest positive number, N=33.

Gari Chua - 7 years, 6 months ago

Why do you need to find x , y x,y in the first place as far as the problem is concerned? Also we are asked for the minimum N, so if N is a multiple of 33, then what would be the minimum N? 33 of course, right? Even if you want to find x , y x,y , then 61 x + 94 y = 1 61x+94y=1 will have a solution as g c d ( 61 , 94 ) = 1 gcd(61,94)=1 can be expressed as a linear combination of 61,94 .

Jit Ganguly - 7 years, 6 months ago

another method

Ali Fareed - 7 years, 6 months ago

On trying x=6 and y= -4 I get N = 30, which is <33 ??

Ayush Kumar - 7 years, 6 months ago

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Something must have gone wrong, because N N is necessarily a multiple of 33 33 .

Daniel Liu - 7 years, 6 months ago

Wrap your math equations in \ ( \ ) instead of \ [ \ ]. That would fix your 'alignment issue'.

Mursalin Habib - 7 years, 6 months ago

It is not so much d divides ax + by but that:

ax + by = d for some integers x and y

Star Light - 7 years, 6 months ago

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Please elaborate, I mean why "it is not so much d divides ax+by but that :................" . d is the gcd right?

Jit Ganguly - 7 years, 6 months ago

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There might be a many combinations of numbers that satisfies the equation.

Praneeth Goud - 7 years, 6 months ago

Dear Math Slayer, there may be more than 1 pair of (x,y). Ithink u can get them jst by trail and error or the euclidean algorithm

Sagnik Saha - 7 years, 6 months ago

here is my finding...

2013-> 3 x 11 x 61

3102-> 2 x 3 x 11 x 47

if one has to find x and y then clearly

3 x 11(61x + 94y)

minimize the brackets part multiplied by 33 will be the answer, and it's minimum value can be 1

but wait.. how can you be so sure that you can achieve 1 with the bracket expression. If there is any standard theorem then please let me know. *I need proof *

Tarun Chabarwal - 7 years, 6 months ago

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Well mate, there always exists a solution to the equation in the bracket, given the condition that the co-efficient of of x,y are co-prime to each other.

Jit Ganguly - 7 years, 6 months ago

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It's called Bezout's Lemma. The process used to get the solution is called the (extended) Euclidean Algorithm.

Michael Tang - 7 years, 6 months ago

hey guys just review my solution please...2013 x+3012y=N 2013(x+y)+999 y=N let x=3 and y=-2 2013-1998=N=15 so N=15 right????

Rohin Raj - 7 years, 6 months ago

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its 3102 y in the question not 3012 as you have stated

Akash Jain - 7 years, 6 months ago

well can u make out if any of the x, y that gives N=33

Kipa Tachak - 7 years, 6 months ago

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I mean you want to find the x,y for which the equation holds? Scroll down someone found the values.

Jit Ganguly - 7 years, 6 months ago

Easy method: I used brute-forced method using python, I made an assumptions for both x and y, values ranging from -100 to 100. I created an array ARR as container of the possible values of N, where N=2013 x+2013 y. Then, I used the minimum function "min" and min(ARR)=33. Lastly, I put it on the answer box and gotcha it is the correct answer.

Mharfe Micaroz - 7 years, 6 months ago
Kishlaya Jaiswal
Nov 25, 2013

We'll try to see a more general case -

By the Euclidean algorithm, we know that g c d ( a , b ) = a x + b y gcd(a,b) = ax + by

We know that g c d ( a , b ) gcd(a,b) gives us the smallest value of a x + b y ax+by for any integers x x and y y

Hence, in particular the smallest value of N = 2013 x + 3102 y N = 2013x+3102y would definetely be g c d ( 2013 , 3102 ) gcd(2013,3102)

Now 2013 = 3 × 11 × 61 2013 = 3\times11\times61 and 3102 = 2 × 3 × 11 × 47 3102 = 2\times3\times11\times47 , so g c d ( 2013 , 3102 ) gcd(2013,3102) turns out be 33 33

Hence, the smallest value of N = 33 N = \boxed{33}

Is it always that g c d ( a , b ) = a x + b y gcd(a,b) = ax+by or such that there exist integers x,y such that g c d ( a , b ) = a x + b y gcd(a,b) = ax+by . So you mean to say
a x + b y ax+by always gives the gcd?

Jit Ganguly - 7 years, 6 months ago

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N is not 33 but multiple of 33 to get N = 33, (61x + 94y) = 1 I found (61x + 94y) = 5 so N = 165

x = – 3 and y = 2

Sunil Pradhan - 7 years, 6 months ago

I mean to say that there exists integers x , y x,y

such that g c d ( a , b ) = a x + b y gcd(a,b) = ax+by

Kishlaya Jaiswal - 7 years, 6 months ago

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Yes that's right.

Jit Ganguly - 7 years, 6 months ago

Thanks for easy method

Selva Vignesh - 7 years, 6 months ago

least value must be obtained from the difference of 2013x and 3102y. since if x is -1 and y=1, difference will be 1089. To make this value smaller, take it, multiplied by 2 and minus 2013, we have 165. 165 multiplied by 19 or multiplied by 12, take 2013-165 12 or 165 19-3102 to obtain 33...

Wu Zhou - 7 years, 6 months ago
Labib Rashid
Nov 27, 2013

According to Bezout's Lemma, the minimum positive value that can be written in the given form has to be the GCD of the integers (2013, 3012) . GCD of the numbers is 33 . Therefore the solution is 33 .

Arkan Megraoui
Nov 25, 2013

By Bezout's lemma the smallest possible positive N is gcd(2013, 3102)=33.

probably the best method like Guinness, probably the best beer

Wu Zhou - 7 years, 6 months ago

What is Bezout's lemma?

Christopher Boo - 7 years, 6 months ago

Well, the gcd between 2013 2013 and 3102 3102 is 33 33 , therefore 33 N 33 | N , i.e.,

33 × k = N > 0 k = 1 N = 33 33 \times k = N > 0 \therefore k = 1 \Rightarrow N = 33

x=38 and y=(-24)

2013x38+3102x(-24)=74484-74481=33

umhhh nice

Naveed Aslam - 7 years, 6 months ago
Rik Ghosh
Nov 27, 2013

we know that gcd(a,b) can be written as ax+by for integers x,y hence 2013x+3102y = gcd(2013,3102) which is the least N..

Rohit Kanrar
Nov 26, 2013

From theorem we get, g c d ( a , b ) = a x + b y gcd(a,b)=ax+by for any integer x and y.

In the above problem, 2013 x + 3102 y = N 2013x+3102y=N can be written as, g c d ( 2013 , 3102 ) = N gcd(2013,3102)=N .

By further simple calculation it can be calculated that g c d ( 2013 , 3102 ) = 33 gcd(2013,3102)=33

Therefore The answer is N = 33 N=\boxed{33} .

A simple Diophantine Equation, Find gcd of the coeficients and you get the answer !

Sean Gee
Dec 7, 2013

The greatest common divisor of a and b is the smallest positive linear combination of a and b .

Ahaan Rungta
Dec 3, 2013

It is a known fact of the Euclidean Algorithm that the smallest positive value of N N such that there exists (not necessarily positive) integers x x and y y satisfying a x + b y = N ax + by = N is gcd ( a , b ) \text {gcd}(a,b) .

Thus, the answer is gcd ( 2013 , 3102 ) = 33 . \text{gcd}(2013,3102) = \boxed{33}.

gud

Naveed Aslam - 7 years, 6 months ago

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