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## #1 2006-10-19 05:51:30

Jaswahhihi
Member
Registered: 2005-07-23
Posts: 11

### Congurences

Hi.

Can anyone do this question and explain how you get the answer please?

Thanks

Determine whether or not there is a solution; if there is, find the General Solution.

18x = 21 mod 25

EDIT -(Oh and if that doesnt have a solution heres another:

6x = 5 mod 13)

Last edited by Jaswahhihi (2006-10-19 05:52:35)

98% of the teenage population does or has tried smoking pot. If you're one of the 2% who hasn't, copy & paste this into your signature.

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## #2 2006-10-19 06:57:35

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

### Re: Congurences

18x = 21 mod 25

You know that 18 = -7 mod 25 and 21 = -4 mod 25, so the problem becomes:

-7x = -4 mod 25

Which means:

25 | -7x + 4

Now find an x which statisfies this.

98% of the teenage population does or has tried smoking pot. If you're one of the 2% who hasn't, copy & paste this into your signature.

98% of the teenage population believes the myth that 98% of the teenage population has smoked pot.  If you're one of the 2% who doesn't believe this, copy & paste this into your signature.

"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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## #3 2006-10-19 07:47:53

Jaswahhihi
Member
Registered: 2005-07-23
Posts: 11

### Re: Congurences

ah no mate, Im just after getting the origonal expression: ax=b mod m

into the form:

x = c mod m'

where apparently m' = m/hcf(a,m)

Lol, I havent logged onto this forum in a few years, I didnt reaslise I still had that siggy

98% of the teenage population does or has tried smoking pot. If you're one of the 2% who hasn't, copy & paste this into your signature.

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## #4 2006-10-19 10:21:23

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

### Re: Congurences

98% of the teenage population doesn't collect pots.

Why did the vector cross the road?
It wanted to be normal.

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## #5 2006-10-19 17:49:53

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

### Re: Congurences

Ricky wrote:

98% of the teenage population believes the myth that 98% of the teenage population has smoked pot.  If you're one of the 2% who doesn't believe this, copy & paste this into your signature.

actually, roughly 80% of teens i know, do or have indeed tried pot.

The Beginning Of All Things To End.
The End Of All Things To Come.

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## #6 2006-10-19 18:33:27

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

### Re: Congurences

First off, how do you judge 80%?  Did you count?  And how do you know they are telling the truth?

Most studies, it's around 40-45%.

Jaswahhihi, I'm confused at what you actually want.  I thought you wanted to solve for x.  Is this incorrect?

"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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## #7 2006-10-22 06:24:01

Jaswahhihi
Member
Registered: 2005-07-23
Posts: 11

### Re: Congurences

Yeh I needed a general solution.

But Its ok now, went to a help lecture and got the info I needed.

Thanks for the input though
(on my sig aswell )

98% of the teenage population does or has tried smoking pot. If you're one of the 2% who hasn't, copy & paste this into your signature.

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