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

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

### Congurences

Hi.

Having real problems understading my lecutre notes about this.

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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