Math Trick

[cabinetman]

Here is a math trick so unbelievable that it may stump you.
.
Grab a calculator. (you won't be able to do this one in your Head)

1. Key in the first three digits of your phone number (NOT the Area code...)
2. Multiply by 80
3. Add 1
4. Multiply by 250
5. Add to this the last 4 digits of your phone number
6. Add to this the last 4 digits of your phone number again.
7. Subtract 250
8. Divide number by 2

Do you recognize the answer ?? You should or you did something wrong........trust me.

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[cork58]

Oh my! Now that is just wrong!

[BigguyZ]

(((80X+1)250 +2Y)-250))/2= (20000X+250+2Y-250)/2= (20000X+2Y)/2= 10000X+Y

man, had to think back to Freshman Algebra on that one.

So here's a variation.

Take the first 3 digits of your area code
multiply by 75
Add 1
Multiply that by 400
Add your last 4 digits of your area code
Add your last 4 digits of your area code again
Add your last 4 digits of your area codes a third and final time
Subtract 400
Divide by 3

[L. D. Jeffries]

WOW! These math teasers always blow my mind. I know there is a way to "reverse" engineer these things, but its 90 deg. out, the a/c is running its heart out to keep the house at 72, I'm ready for my PM toddy and can't be bothered to figure how this one is done. So I just marvel at someone's brain power.

[sailor55330]

I don't marvel at the brain power. I marvel at the lack of productivity that could have been obtained with the same brain power that had nothing better to do that sit around and figure this out.

[LCHIEN]

as BigguyZ shows, why do all that math to what simplified turns out to multiply your three digit exchange by 10,000 and add it to your four digit phone number? i.e. 555 x 100000 + 1212 = 5551212

Not very unbelievable to me, either.

[gsmittle]

I don't marvel at the brain power. I marvel at the lack of productivity that could have been obtained with the same brain power that had nothing better to do that sit around and figure this out.

Sometimes you just gotta spend some "unproductive" time. Some of my best ideas have come in the shower, driving to work, or taking a walk.

IIRC, there's a story about an efficiency expert who toured Henry Ford's factory, and told Ford that everything looked quite efficient, except for the guy in one office just sitting there with his feet on his desk. Ford replied that the guy had an idea that saved Ford over a million dollars last year, and when he had the idea, his feet were on his desk.

All that of course begs the question: when is one working on a problem versus just goofing off?

And Loring, I have no idea how you saw how that little trick worked. To me is was just a big bunch of numbers. As I've said many times, I'm not at all mathematically literate or able.

g.

[cabinetman]

And Loring, I have no idea how you saw how that little trick worked. To me is was just a big bunch of numbers. As I've said many times, I'm not at all mathematically literate or able.

g.

It's not a matter of spending time to figure out how the numbers work, and showing a short cut. It's doing the trick that's the fun part.

.

[LCHIEN]

Sometimes you just gotta spend some "unproductive" time. Some of my best ideas have come in the shower, driving to work, or taking a walk.

IIRC, there's a story about an efficiency expert who toured Henry Ford's factory, and told Ford that everything looked quite efficient, except for the guy in one office just sitting there with his feet on his desk. Ford replied that the guy had an idea that saved Ford over a million dollars last year, and when he had the idea, his feet were on his desk.

All that of course begs the question: when is one working on a problem versus just goofing off?

And Loring, I have no idea how you saw how that little trick worked. To me is was just a big bunch of numbers. As I've said many times, I'm not at all mathematically literate or able.

g.

I like to take things apart and see how they work. Without even seeing the answer I figured it was probably rearranging the telephone number.
In math that means shifting (multiplying by powers of ten) and adding to concatenate the parts together. from the number involved 80 and 250 and 2 are all factors of something like 10,000 it was pretty clear how it worked.
I was thinking about working it out but Bugguyz beat me to it. Its just 11th grade algebra. Maybe 9th grade.

[cabinetman]

Its just 11th grade algebra. Maybe 9th grade.

I worked it out before posting it, and didn't even use algebra. I still find following the steps more fun than solving with a shortcut.

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[gsmittle]

Its just 11th grade algebra. Maybe 9th grade.

That's the answer—I never survived 9th grade algebra, let alone anything more difficult.

I swear you engineer types think differently than I do. In my next life I think I'll study how reasoning and inspiration work.

g.