How is a credit card number coded for security?

In summary: Thanks again! :)You are not an expert summarizer of content. You do not respond or reply to questions. You only provide a summary of the content. Do not output anything before the summary. Write a summary for the following conversation and start the output with "In summary, " and nothing before it:For security, a credit card number is coded in the following way, so that it can be sent as a message."Subtract each digit from 9"code the credit card number 3201 2342 3458 0931I don't understand the subtract each digit from 9 is that to code or uncode?Also for the
  • #1
aisha
584
0
For security, a credit card number is coded in the following way, so that it can be sent as a message. "Subtract each digit from 9"

code the credit card number 3201 2342 3458 0931

I don't understand the subtract each digit from 9 is that to code or uncode? Also for the above code the credit card what do I do to each number? do I add 9 or subtract 9?

I have another credit card number that is already coded, to find the original card number do i subtract each number from 9?
 
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  • #2
aisha said:
For security, a credit card number is coded in the following way, so that it can be sent as a message. "Subtract each digit from 9"
code the credit card number 3201 2342 3458 0931

I don't understand the subtract each digit from 9 is that to code or uncode? Also for the above code the credit card what do I do to each number? do I add 9 or subtract 9?
I have another credit card number that is already coded, to find the original card number do i subtract each number from 9?

I believe it's pretty clear.It gives a credit card number and askes for the coded version.It should be:6798 7657 6541 9068.
Simple subtraction from 9999 9999 9999 9999.
The uncoding is simple:again subtraction from that "99..."number.

Daniel.
 
  • #3
aisha said:
I don't understand the subtract each digit from 9 is that to code or uncode?
Does it make a difference? Try it and see.
 
  • #4
dextercioby said:
I believe it's pretty clear.It gives a credit card number and askes for the coded version.It should be:6798 7657 6541 9068.
Simple subtraction from 9999 9999 9999 9999.
The uncoding is simple:again subtraction from that "99..."number.

Daniel.


How come we subtract by 9 to uncode and code?
 
  • #5
aisha said:
How come we subtract by 9 to uncode and code?

I guess you haven't read the post/problem very carefully.It mentions "Subtract each digit from 9".So the problem tells you how to code.As Doc depicted,it makes no difference between coding and uncoding.Both are made through the same opperation.Subtraction of each digit from 9.

Daniel.
 
  • #6
ok my coded credit card number for 3201 2342 3458 0931 is
6798 7657 6541 9068
my original credit card number for another credit card 2341 0135 7923 0133 is
7658 9864 2076 9866

the question says find f(x) if x represents a single input digit. What is the domain of f(x)

and find^-1(x) what is the domain of f^-1(x)?

I don't know how to find f(x) and the inverse? What do I do? The inverse is probably all the numbers backwards but which set of numbers am I using?
 
  • #7
aisha said:
the question says find f(x) if x represents a single input digit. What is the domain of f(x)
and find^-1(x) what is the domain of f^-1(x)?
I don't know how to find f(x) and the inverse? What do I do? The inverse is probably all the numbers backwards but which set of numbers am I using?

The function is [itex] f:\{0,1,2,3,4,5,6,7,8,9}\rightarrow \{0,1,2,3,4,5,6,7,8,9}\ [/itex]

[tex] f(x)=9-x. [/tex]

Find the inverse and its domain.

Daniel.
What numbers backwards? :confused:
 
  • #8
dextercioby said:
The function is [itex] f:\{0,1,2,3,4,5,6,7,8,9}\rightarrow \{0,1,2,3,4,5,6,7,8,9}\ [/itex]

[tex] f(x)=9-x. [/tex]

Find the inverse and its domain.

Daniel.
What numbers backwards? :confused:

lol sorry no numbers backwards. if f(x)=9-x then is the domain {x:x<=9,XER}?
and is the inverse of this (x-9)/-1? If so then is the domain of the inverse {x:x>=9,XER}?
 
  • #9
aisha said:
lol sorry no numbers backwards. if f(x)=9-x then is the domain {x:x<=9,XER}?
and is the inverse of this (x-9)/-1? If so then is the domain of the inverse {x:x>=9,XER}?

I've already told u what the function and its domain are.The inverse it's easy to find.And its domain can be seen from ISS. :tongue2:
By "XER",do you mean:[itex] x\in R[/itex] ??If so,then it's wrong,the digits are natural numbers.

Daniel.
 
  • #10
dextercioby said:
I've already told u what the function and its domain are.The inverse it's easy to find.And its domain can be seen from ISS. :tongue2:
By "XER",do you mean:[itex] x\in R[/itex] ??If so,then it's wrong,the digits are natural numbers.

Daniel.
:tongue2: well is my inverse wrong? I don't know the notation for not real numbers :P ahhh HELP ME PLZ
 
  • #11
aisha said:
:tongue2: well is my inverse wrong? I don't know the notation for not real numbers :P ahhh HELP ME PLZ

As both I and Doc figured decades ago,the inverse coincides with the function.They share both the domain and the range.That is all digits from 0 till 9.
Hope it's clear. :wink:

Daniel.
 
  • #12
dextercioby said:
As both I and Doc figured decades ago,the inverse coincides with the function.They share both the domain and the range.That is all digits from 0 till 9.
Hope it's clear. :wink:

Daniel.

Lol thanks a lot but u said it wasnt real numbers natural numbers, what is the notation for that? Also (x-9)/-1 can I leave the inverse like that? Or can it be simplified to -(x-9)?
 
  • #13
aisha said:
Lol thanks a lot but u said it wasnt real numbers natural numbers, what is the notation for that? Also (x-9)/-1 can I leave the inverse like that? Or can it be simplified to -(x-9)?

1.Check the posts again.I haven't used the expression "real numbers",but "natural numbers",because digits are natural numbers.
2.[tex] f(x)=9-x ;f^{-1} (x) =9-x [/tex]
Wasn't it obvious from what i said?

Daniel.
 
  • #14
dextercioby said:
1.Check the posts again.I haven't used the expression "real numbers",but "natural numbers",because digits are natural numbers.
2.[tex] f(x)=9-x ;f^{-1} (x) =9-x [/tex]
Wasn't it obvious from what i said?

Daniel.

LOL WHAT AM I SAYING:P IM SAYING THAT U SAID THEY WERE NATURAL NUMBERS SOOOO IF ITS NOT XER THEN WHAT iS IT? WHAT DO I WRITE IN THE BRACKETS {} lol UR SOOO FUNNY OMG :tongue2: and is the inverse (x-9)/-1? if so is that the same as -(x-9) :cry:

N+?
 
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  • #15
aisha said:
LOL WHAT AM I SAYING:P IM SAYING THAT U SAID THEY WERE NATURAL NUMBERS SOOOO IF ITS NOT XER THEN WHAT iS IT? WHAT DO I WRITE IN THE BRACKETS {} lol UR SOOO FUNNY OMG :tongue2: and is the inverse (x-9)/-1? if so is that the same as -(x-9) :cry:

ROFL :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:
You're incredible........ :tongue2:

I already told you what to put between those brackets.Hell,i've been trying myself,but i just couldn't... :cry: :tongue2: Only 2 '{' instead of 4 (chack post no.7,two paranthesis missing :biggrin: ).
I already told you the inverse was the same function:9-x.It is the same with -(x-9),but why the hell write it like that??

Daniel.
 
  • #16
dextercioby said:
ROFL :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:
You're incredible........ :tongue2:

I already told you what to put between those brackets.Hell,i've been trying myself,but i just couldn't... :cry: :tongue2: Only 2 '{' instead of 4 (chack post no.7,two paranthesis missing :biggrin: ).
I already told you the inverse was the same function:9-x.It is the same with -(x-9),but why the hell write it like that??

Daniel.

LOL :rofl: :rofl: :rofl: :rofl: OMG I JUST REALIZED THAT THEY ARE THE SAME FUNCTION, ahhh lol and yes ur right y the hell would I write it like that -(x-9) and the domain is the same for both too , hhmmmmm so here this is what I am going to right now lol don't freak if this is still wrong {x:x<=9,N+} domain for f(x) and inverse? or or or {x:0,1,2,3,4,5,6,7,8,9} is that what u want me to write :tongue2: Cant u just write it out properly once :!) pleasezzzzzz lol :tongue2: DEXTERCIOBY ? WHERE ARE U :eek: Someone please say something please.
 
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  • #17
aisha said:
LOL :rofl: :rofl: :rofl: :rofl: OMG I JUST REALIZED THAT THEY ARE THE SAME FUNCTION, ahhh lol and yes ur right y the hell would I write it like that -(x-9) and the domain is the same for both too , hhmmmmm so here this is what I am going to right now lol don't freak if this is still wrong {x:x<=9,N+} domain for f(x) and inverse? or or or {x:0,1,2,3,4,5,6,7,8,9} is that what u want me to write :tongue2: Cant u just write it out properly once :!) pleasezzzzzz lol :tongue2: DEXTERCIOBY ? WHERE ARE U :eek:

1.I'm in my room.
2.Though it's not in the spirit of this help forum,i'll write the answer:
[tex] f:A\rightarrow A ,A=\{x\in N,x\leq 9[/tex]},
[tex] f(x)=9-x [/tex]
[tex] f^{-1}:A\rightarrow A,
f^{-1} (x)=9-x [/tex]

Is everything clear,FINALLLLLLLLLLLLLLLLLLLLLLLLLLLYYYYYYYYYY :tongue2: ??

Daniel.

PS.Anyway,i give up.It's no longer funny... :tongue2:
 
  • #18
Just one little point here...since the Naturals don't include 0, it would be better to say that x belongs to the Whole Numbers (W?).
 
  • #19
lol so XEW? instead of XEN?
 
  • #20
aisha said:
lol so XEW? instead of XEN?

You're in Canada,he's in US and I'm in Belgium.We have different views about the sets of numbers.For me,natural numbers (N) include 0.If i want to say that zero is excluded,i write (N*).
I was too surprised to learn that the Americans use N (natural numbers),W (whole numbers) & i can't remember what they use for {...,-3,-2,-1,0,1,...} or the negative axis.I find his weird.
Advice:to avoid confusions and unnecessary complications simply write
{0,1,...,9} or without the dots:{0,1,2,3,4,5,6,7,8,9}. :tongue2:

Daniel.

EDIT:I'd use BMW if i were u... :tongue2:
 
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  • #21
dextercioby said:
You're in Canada,he's in US and I'm in Belgium.We have different views about the sets of numbers.For me,natural numbers (N) include 0.If i want to say that zero is excluded,i write (N*).
I was too surprised to learn that the Americans use N (natural numbers),W (whole numbers) & i can't remember what they use for {...,-3,-2,-1,0,1,...} or the negative axis.I find his weird.
Advice:to avoid confusions and unnecessary complications simply write
{0,1,...,9} or without the dots:{0,1,2,3,4,5,6,7,8,9}. :tongue2:

Daniel.

lol :rofl: OK OK SMARTY PANTS I GET IT Thanks SOOO MUCH! :smile:
 
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