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#1 2012-10-12 19:51:12
- Harold
- Guest
Modulo
Can you help me with these two problem
-23 mod 5
23 mod -5
and,could you please explain modulo with nagetive number?
#2 2012-10-12 20:20:23
- bobbym
- Administrator
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Re: Modulo
Hi;
If you use this formula you will have no problems with modulo.
Where
is called the floor function and is evaluated like this:
and
it always rounds down to the smallest integer.
Let's do the first one:
-23 mod 5
You are looking for r, the remainder. a = -23 and m is the modulo, in this case 5.
Now
So -23 mod 5 is 2.
You try the second one. Let me know what you get.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#4 2012-10-12 22:21:10
- bobbym
- Administrator
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Re: Modulo
Hi;
Yes, unless you are told it must be positive.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#6 2012-10-12 23:07:52
- bobbym
- Administrator
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Re: Modulo
Hi;
You are welcome. Were you able to do the second problem?
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#7 2012-10-12 23:50:15
- bob bundy
- Moderator
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Re: Modulo
hi bobbym,
Yes he has (in post 3). He got -2
The definition for modulo regarding + or - is uncertain. See http://en.wikipedia.org/wiki/Modulo_operation
Harold ought to check how it has been defined by his teacher.
Bob
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
#8 2012-10-13 00:10:13
- bobbym
- Administrator
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Re: Modulo
Hi;
Yes he has (in post 3). He got -2
I see that now. He got the right answer too.
Sometimes it has to be the same sign as the divisor. I gave him the one that gets the same answers as Wolfram would.
Unfortunately he skeddadled right after he solved it. I wanted to go a little deeper.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#9 2012-10-13 02:21:18
- Harold
- Guest
Re: Modulo
Guys,I have another problem,my brother says that 23 mod -5 will be 3 as Euclidean division states a=bq+r and the division will be 23=(-5)*(-4)+3.
#10 2012-10-13 03:15:27
- bob bundy
- Moderator
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Re: Modulo
hi Harold,
In effect, that was my point in post 7.
The following are all equivalent mod 5
-12, -7, -2, 3, 8, 13, 18 ......
Basically just add 5.
If you follow my link to Wiki you will see that two definitions are possible and there are even more variations amongst computer languages.
Your brother is right using the 'Euclidean division' definition ... under this no negatives are allowed.
Which is why I think you need to check with your teacher / tutor and see what definition is required.
Bob
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
#11 2012-10-13 19:30:24
- Harold
- Guest
Re: Modulo
I am sorry to bug again but after you gave me the formula,i experimented a little and solution to -23 mod -5 results -43,is it correct
#12 2012-10-13 20:24:25
- bobbym
- Administrator
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Re: Modulo
Hi;
I am getting -3 as the answer. Can I see what you have done?
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#14 2012-10-13 21:00:24
- bobbym
- Administrator
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Re: Modulo
Hi;
I am getting
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#15 2012-10-13 22:43:55
- Harold
- Guest
Re: Modulo
You're right,i missed a minus sign,thank you a lot,you guys taught me a lot of things today.
#16 2012-10-13 22:49:15
- bobbym
- Administrator
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Re: Modulo
Hi Harold;
Use a calculator to at least check.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#18 2012-10-14 20:37:55
- bobbym
- Administrator
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Re: Modulo
Hi bob;
If you did that what do you get for -65 mod -17?
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#20 2012-10-14 21:02:32
- bobbym
- Administrator
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Re: Modulo
Hi Bob;
Good Morning.
That is what I am getting too.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#22 2012-10-14 21:11:05
- bobbym
- Administrator
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Re: Modulo
Hi;
Yes, it is an obvious error, the answer can never exceed m. In either direction.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.