Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

I like to post on how to be a better problem solver. From my point of view this is way more important than being good at math. Many math types are not good problem solvers. Instructing a student in calculus or number theory is a job for the school system. But since you are asking I will give you what I have about mods and congruences if you have the time.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

Yes I have the time. I want to be a better problem solver, but I can't solve a problem when I don't have the maths required to solve it. Like brittle math 2 for example, I have to know about v = d/t but I can solve Brittle Math 1 because no maths is required.

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

The mod operator returns the remainder when one number is divided by another.

For instance:

5 mod 3 is 2 because when 5 is divided by 3 there is a remainder of 2.

37 mod 9 is 1 because when 37 is divided by 9 there is a remainder of 1.

8 mod 2 is 0 because when 8 is divided by 2 there is a remainder of 0.

Do you follow that?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

nvm got it. I saw 85 just now

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Okay, you do a few:

123 mod 11 is ?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

2

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

That is correct. What is

5^3 mod 10 ?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

5

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

What is 6^4 mod 100 ?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

96

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

That is correct. What is 10^19 mod 10 ?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

0

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

That is correct. We write mods in this way.

When we say 13 mod 2 = 1 we write that as

this is read as 13 is congruent to 1 mod 2.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

I got that

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

123 mod 11 = 2 is written

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

I got that too

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Okay then what does this say

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

100 is congruent to 0 mod 10

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

In ordinary words what does it mean?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

100 is same to mod 10

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Not quite, it means 100 leaves a remainder of 0 when divided by 10. This is another way of saying 10 divides 100.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

Oh

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Did you notice that taking mod 10 of any number gets the last digit?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,135

Yes

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

So taking the mod 10 of this

should get the last digit.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline