Cool Math Trick

[EvoN1020v]

Here is an extradiotary cool math trick. Try it yourself!

 

1. Grab a calculator (You won't be able to do this one in your head)

2. Key in the first three digits of your phone number (NOT the area code)

3. Multiply by 80

4. Add 1

5. Multiply by 250

6. Add the last 4 digits of your phone number

7. Add the last 4 digits of your phone number again

8. Subtract 250

9. Divide number by 2

 

Do you recognize the answer?

 

It's like magic, eh?

[5614]

Nice one, I like it.

[cosine]

Here is an extradiotary cool math trick. Try it yourself!

 

1. Grab a calculator (You won't be able to do this one in your head)

2. Key in the first three digits of your phone number (NOT the area code)

3. Multiply by 80

4. Add 1

5. Multiply by 250

6. Add the last 4 digits of your phone number

7. Add the last 4 digits of your phone number again

8. Subtract 250

9. Divide number by 2

 

Do you recognize the answer?

 

It's like magic' date=' eh? [/quote']

 

[hide]

Cute, I like how steps 4 and 8 cancel each other out.

And then how 3,5, and 9 combine to just shift over the first 3 digits.

Did you come up with that one? I love analyzing them, hope you don't mind.

[/hide]

 

Here's one that I came up with a while ago:

1. Think of any two digit number.

2. Add the two digts and subtract the sum from your original number.

3. Divide this difference by the first digit of your original number.

4. Triple this quotient, and subtract 2.

 

Did you arrive at 25?

[swansont]

It's like magic' date=' eh? [/quote']

 

 

No, more like algebra.

 

But to paraphrase Clarke's third law, to any sufficiently math illiterate society, associative, commutative and distributive properties are indistinguishable from magic.

[EvoN1020v]

Cute, I like how steps 4 and 8 cancel each other out.

And then how 3,5, and 9 combine to just shift over the first 3 digits.

Did you come up with that one? I love analyzing them, hope you don't mind.

 

I'm impressed with Cosine's analyzination. I wasn't expecting anyone to really read it hard. I was just providing it for entairment, but thanks anyway.

 

But to paraphrase Clarke's third law, to any sufficiently math illiterate society, associative, commutative and distributive properties are indistinguishable from magic.

 

Relate to swansont's reply, I was using the word "magic" metaphorically. Don't you understand that English can have some abrasct imagery. I don't expect any cricitism about English. Plus, English is my second language, so whatever.

 

[cosine]

I'm impressed with Cosine's analyzination. <snip>

 

Thanks!

[CanadaAotS]

I did arrive at 25... lol

 

[hide]

x = first digit, y = second digit

Think of a 2 digit number : 10x + y

Add digits and subtract from number : 10x + y - (x + y) = 10x - x

Divide by the first digit of your number : (10x - x) / x = 9

Multiply by 3 : 9 * 3 = 27

Subtract 2 : 27 - 2 = 25

I got 25! lol

[/hide]

 

EDIT: I like breaking these things down to lol

[cosine]

I did arrive at 25... lol

 

[hide]

x = first digit' date=' y = second digit

Think of a 2 digit number : 10x + y

Add digits and subtract from number : 10x + y - (x + y) = 10x - x

Divide by the first digit of your number : (10x - x) / x = 9

Multiply by 3 : 9 * 3 = 27

Subtract 2 : 27 - 2 = 25

I got 25! lol

[/hide']

 

EDIT: I like breaking these things down to lol

 

haha yeah... I was first making it and I was like... how to manipulate it to get rid of the actual variables? then you would have whatever number came out, every time, then you would always know the answer.

[Tokoyami]

haha nice

[NPK]

Here is an extradiotary cool math trick. Try it yourself!

 

1. Grab a calculator (You won't be able to do this one in your head)

2. Key in the first three digits of your phone number (NOT the area code)

3. Multiply by 80

4. Add 1

5. Multiply by 250

6. Add the last 4 digits of your phone number

7. Add the last 4 digits of your phone number again

8. Subtract 250

9. Divide number by 2

 

Do you recognize the answer?

 

It's like magic' date=' eh? [/quote']

Nope, don't recognise the number. Do you have to have an American phone number for it to work?

[matt grime]

Relate to swansont's reply' date=' I was using the word "magic" metaphorically. Don't you understand that English can have some abrasct imagery. I don't expect any cricitism about English. Plus, English is my second language, so whatever.

 

[/quote']

 

This is a maths forum, presumably hoping to attract mathematically competent people to discuss things that are reasonably mathematical. Sadly almost every single post on mathematics in it has been either crackpottery or very elementary, but such is the nature of mathematics and the level that is taught in most universities these days that this is almost inevitable.

 

If you post some trivial manipulation then don't expect people to be particularly impressed with it, at least not from those who have higher hopes of the forum and have bad experiences with some posters and society in general when it comes to maths: maths is, sadly, too often treated as a black art that it is acceptable to have no knowledge of, and in a forum dedicated to it no one needs to compound this misapprehension.

 

I didn't see anyone criticize your English. Merely the choice of the word 'magic', and I could add 'extraordinary' and 'cool', thus proving the first law of mathematics forums:

 

any post whose title contains some of the words 'hard', 'amazing', 'cool', or 'impossible' is invariably not.

[Deified]

I'll admit I was a bit surprised when I saw my phone number appear on my TI-83 (yea I know I'm behind the times, but I'm not exactly loaded either) but once I analyzed it algebraically it became painfully obvious. The whole thing is transparent in algebraic terms. My analyzation:

 

x=first three numbers

y=last four

 

The whole process on one line: ((80x + 1) * 250 + y + y - 250) / 2

Simplify and unparenthesize: (20 000x + 250 + 2y - 250) / 2

Simplify: 10 000x + y

Example: 10 000(578) + 0861 = 5780000 + 0861 = 5780861 Which is of course a theoretically possible phone number (in the US).

 

I can actually imagine something like this being used to teach algebra one. It's not difficult to analyze but you have to think about it algebraically. Something many people are not capable of doing. I agree with matt_grime. We need a society that values scientific knowledge and mathematical abilities as much as knowledge of classical composers or famous artists. But even that is not enough, we need a society that values scientific interest above interest in sports, knowledge of movies and knowing every single song on the current top 50 charts. I wonder if such a thing is even possible?

[cosine]

I'll admit I was a bit surprised when I saw my phone number appear on my TI-83 (yea I know I'm behind the times, but I'm not exactly loaded either) <snip>

 

Haha, I usually work things out by hand. Then sometimes I'll use a compass and straightedge, then a slide rule, and my last choice is to use my TI-30X II Dual-Line.

[doG]

then a slide rule

Yeah, which model? Mine's a K&E Duplex Decitrig.....

[cosine]

Yeah, which model? Mine's a K&E Duplex Decitrig.....

 

Mine is a Pickett N902-ES, A Simplex Trig metal slide rule.

[SkyQueen737]

That's pretty neat.

[NPK]

...

[Kyle]

Do you recognize the answer?

 

It's like magic' date=' eh? [/quote']

 

Wow! How did it guess my birthday!?

[cosine]

Wow! How did it guess my birthday!?

Hahahaha!

 

Independence is always subject to satirical parody.