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What is the smallest number n> 5 so that 5 ^ n ends with “3125”?

How to prove that if $aequiv b pmodkn$ then $a^kequiv b^k pmodk^2n$Horizontal tank with hemispherical ends depth to capacity calculationDoes the smallest real number that satisfies $2^xge bx$ have logarithmic order?Determine the smallest number POptimization, find the dimensions of the poster with the smallest areaIs $s(t) = 1/(1+t^2)$ a bounded function? If so, find the smallest $M$Continous function approximating the precision of a number.What is the smallest value of this sequence?Find the smallest real number $agt 0$ for which the equation $a^x=x$ has no real solutionsGiven a point A (3,4) What is the smallest segment passing through A and makes a right triangle with the coordinates$f(n) =$ the smallest prime factor of $n$. Prove that the number of solutions to the equation $f(x) = 2016$.

1

$begingroup$

What is the smallest number n> 5 so that 5 ^ n ends with "3125"?

What other examples are there?

calculus

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asked 2 hours ago

Catherine Cooper Catherine Cooper

291

New contributor

Catherine Cooper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  What is your take on this?
  $endgroup$
  – ADITYA PRAKASH
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  Why not just list them out and find it?
  $endgroup$
  – Jair Taylor
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  Why not just do it? It's not $1$ because $5^1=5$. It's not $2$ because $5^2 = 25$. What's to keep you from just continuing?
  $endgroup$
  – fleablood
  2 hours ago
  

  
  
  
  

add a comment | 

1

$begingroup$

What is the smallest number n> 5 so that 5 ^ n ends with "3125"?

What other examples are there?

calculus

share|cite|improve this question

asked 2 hours ago

Catherine Cooper Catherine Cooper

291

New contributor

Catherine Cooper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  What is your take on this?
  $endgroup$
  – ADITYA PRAKASH
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  Why not just list them out and find it?
  $endgroup$
  – Jair Taylor
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  Why not just do it? It's not $1$ because $5^1=5$. It's not $2$ because $5^2 = 25$. What's to keep you from just continuing?
  $endgroup$
  – fleablood
  2 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

What is the smallest number n> 5 so that 5 ^ n ends with "3125"?

What other examples are there?

calculus

share|cite|improve this question

asked 2 hours ago

Catherine Cooper Catherine Cooper

291

New contributor

Catherine Cooper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|cite|improve this question

asked 2 hours ago

Catherine Cooper Catherine Cooper

291

New contributor

Catherine Cooper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|cite|improve this question

asked 2 hours ago

Catherine Cooper Catherine Cooper

291

New contributor

Catherine Cooper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 2 hours ago

Catherine Cooper Catherine Cooper

291

New contributor

Catherine Cooper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 2 hours ago

Catherine Cooper Catherine Cooper

291

4 Answers
4

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4

$begingroup$

So, we are looking for all $n>5$ for which $5^nequiv 3125=5^5mod 10000$.

Note that the following equivalence holds for $n>5$:$$5^nequiv 5^5mod 10000\iff \5^n-4equiv 5mod 16\iff\5^n-5equiv 1mod 16$$Define $mtriangleq n-5ge 1$. Then all the $m$s for which $5^mequiv 1mod 16$ holds are $$m=4kquad,quad kin Bbb N$$this is because $5^4=625equiv 1mod 16$ and therefore $$5^4kequiv5^4k-4equivcdots equiv 5^4equiv 1mod 16$$

Conclusion

All $n>5$s for which $5^n$ ends up with $3125$ can be found from $$n=4k+5quad,quad kin Bbb N$$ and the smallest such $n$ is 9.

share|cite|improve this answer

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

$endgroup$

add a comment | 

2

$begingroup$

Hint: $5^n equiv 5^5 mod 10^4$ if and only if $5^n equiv 5^5 mod 2^4$. What is the multiplicative order of $5$ mod $16$?

share|cite|improve this answer

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

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0

$begingroup$

Well
$$5^9=1953125$$
so the answer is $9$. In fact
$$5^nequiv 5^n-4 mod10^4$$
For $nge 8$, so any value of $5^5+4k$ where $kinmathbbN$ has the last four digits $3125$.

share|cite|improve this answer

edited 2 hours ago

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Why not $5^5 = 3125$.
  $endgroup$
  – fleablood
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  The question states that $ngt5$
  $endgroup$
  – Peter Foreman
  2 hours ago
  

  
  
  
  

add a comment | 

0

$begingroup$

Hint $, 5^large 5+N! bmod 10^large 4 = 5^large 5(5^largecolor#c00 N! bmod 2^large 4).,$ Now recall $, beginalign 5, &equiv 1!pmod! color#c004 \ Rightarrow 5^largecolor#c00 4!&equiv 1^largecolor#c00 4!!!! pmod!color#c004^large 2endalign$

share|cite|improve this answer

edited 4 mins ago

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654

$endgroup$

add a comment | 

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4

$begingroup$

So, we are looking for all $n>5$ for which $5^nequiv 3125=5^5mod 10000$.

Note that the following equivalence holds for $n>5$:$$5^nequiv 5^5mod 10000\iff \5^n-4equiv 5mod 16\iff\5^n-5equiv 1mod 16$$Define $mtriangleq n-5ge 1$. Then all the $m$s for which $5^mequiv 1mod 16$ holds are $$m=4kquad,quad kin Bbb N$$this is because $5^4=625equiv 1mod 16$ and therefore $$5^4kequiv5^4k-4equivcdots equiv 5^4equiv 1mod 16$$

Conclusion

All $n>5$s for which $5^n$ ends up with $3125$ can be found from $$n=4k+5quad,quad kin Bbb N$$ and the smallest such $n$ is 9.

share|cite|improve this answer

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

$endgroup$

add a comment | 

4

$begingroup$

So, we are looking for all $n>5$ for which $5^nequiv 3125=5^5mod 10000$.

Note that the following equivalence holds for $n>5$:$$5^nequiv 5^5mod 10000\iff \5^n-4equiv 5mod 16\iff\5^n-5equiv 1mod 16$$Define $mtriangleq n-5ge 1$. Then all the $m$s for which $5^mequiv 1mod 16$ holds are $$m=4kquad,quad kin Bbb N$$this is because $5^4=625equiv 1mod 16$ and therefore $$5^4kequiv5^4k-4equivcdots equiv 5^4equiv 1mod 16$$

Conclusion

All $n>5$s for which $5^n$ ends up with $3125$ can be found from $$n=4k+5quad,quad kin Bbb N$$ and the smallest such $n$ is 9.

share|cite|improve this answer

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

$endgroup$

add a comment | 

$begingroup$

So, we are looking for all $n>5$ for which $5^nequiv 3125=5^5mod 10000$.

Note that the following equivalence holds for $n>5$:$$5^nequiv 5^5mod 10000\iff \5^n-4equiv 5mod 16\iff\5^n-5equiv 1mod 16$$Define $mtriangleq n-5ge 1$. Then all the $m$s for which $5^mequiv 1mod 16$ holds are $$m=4kquad,quad kin Bbb N$$this is because $5^4=625equiv 1mod 16$ and therefore $$5^4kequiv5^4k-4equivcdots equiv 5^4equiv 1mod 16$$

Conclusion

All $n>5$s for which $5^n$ ends up with $3125$ can be found from $$n=4k+5quad,quad kin Bbb N$$ and the smallest such $n$ is 9.

share|cite|improve this answer

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

$endgroup$

share|cite|improve this answer

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

answered 2 hours ago

Mostafa AyazMostafa Ayaz

17k3939

2

$begingroup$

Hint: $5^n equiv 5^5 mod 10^4$ if and only if $5^n equiv 5^5 mod 2^4$. What is the multiplicative order of $5$ mod $16$?

share|cite|improve this answer

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

$endgroup$

add a comment | 

2

$begingroup$

Hint: $5^n equiv 5^5 mod 10^4$ if and only if $5^n equiv 5^5 mod 2^4$. What is the multiplicative order of $5$ mod $16$?

share|cite|improve this answer

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

$endgroup$

add a comment | 

$begingroup$

Hint: $5^n equiv 5^5 mod 10^4$ if and only if $5^n equiv 5^5 mod 2^4$. What is the multiplicative order of $5$ mod $16$?

share|cite|improve this answer

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

$endgroup$

share|cite|improve this answer

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

answered 2 hours ago

Robert IsraelRobert Israel

328k23216469

0

$begingroup$

Well
$$5^9=1953125$$
so the answer is $9$. In fact
$$5^nequiv 5^n-4 mod10^4$$
For $nge 8$, so any value of $5^5+4k$ where $kinmathbbN$ has the last four digits $3125$.

share|cite|improve this answer

edited 2 hours ago

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Why not $5^5 = 3125$.
  $endgroup$
  – fleablood
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  The question states that $ngt5$
  $endgroup$
  – Peter Foreman
  2 hours ago
  

  
  
  
  

add a comment | 

0

$begingroup$

Well
$$5^9=1953125$$
so the answer is $9$. In fact
$$5^nequiv 5^n-4 mod10^4$$
For $nge 8$, so any value of $5^5+4k$ where $kinmathbbN$ has the last four digits $3125$.

share|cite|improve this answer

edited 2 hours ago

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Why not $5^5 = 3125$.
  $endgroup$
  – fleablood
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  The question states that $ngt5$
  $endgroup$
  – Peter Foreman
  2 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

Well
$$5^9=1953125$$
so the answer is $9$. In fact
$$5^nequiv 5^n-4 mod10^4$$
For $nge 8$, so any value of $5^5+4k$ where $kinmathbbN$ has the last four digits $3125$.

share|cite|improve this answer

edited 2 hours ago

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

$endgroup$

share|cite|improve this answer

edited 2 hours ago

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

answered 2 hours ago

Peter ForemanPeter Foreman

3,8371216

0

$begingroup$

Hint $, 5^large 5+N! bmod 10^large 4 = 5^large 5(5^largecolor#c00 N! bmod 2^large 4).,$ Now recall $, beginalign 5, &equiv 1!pmod! color#c004 \ Rightarrow 5^largecolor#c00 4!&equiv 1^largecolor#c00 4!!!! pmod!color#c004^large 2endalign$

share|cite|improve this answer

edited 4 mins ago

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654

$endgroup$

add a comment | 

0

$begingroup$

Hint $, 5^large 5+N! bmod 10^large 4 = 5^large 5(5^largecolor#c00 N! bmod 2^large 4).,$ Now recall $, beginalign 5, &equiv 1!pmod! color#c004 \ Rightarrow 5^largecolor#c00 4!&equiv 1^largecolor#c00 4!!!! pmod!color#c004^large 2endalign$

share|cite|improve this answer

edited 4 mins ago

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654

$endgroup$

add a comment | 

$begingroup$

Hint $, 5^large 5+N! bmod 10^large 4 = 5^large 5(5^largecolor#c00 N! bmod 2^large 4).,$ Now recall $, beginalign 5, &equiv 1!pmod! color#c004 \ Rightarrow 5^largecolor#c00 4!&equiv 1^largecolor#c00 4!!!! pmod!color#c004^large 2endalign$

share|cite|improve this answer

edited 4 mins ago

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654

$endgroup$

share|cite|improve this answer

edited 4 mins ago

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654

answered 54 mins ago

Bill DubuqueBill Dubuque

212k29195654