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What Happens in Your Brain When You Add 47 and 28?

Vic Mackey

By Vic Mackey
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ABSR

ABSR 5325

Posted
Posted

Simple 47 = 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1

and 28 = 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1

so 75 =  1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1 + 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1

 

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SwanderedTalent

SwanderedTalent 5761

Posted
Posted
On 5/6/2021 at 12:27 AM, ChiTownDoc said:

47+20=67+8=75

 

I can’t be the only one who did that?  And it takes less than 2 seconds.  I was educated only at the finest of institutions.  

That is how I do math as an adult, but not how I was taught in school. I have always been much better at math post-school than I was at it when it was being graded-- I can generally do the four basics in my head in the time it takes most people to get their phone out and pull the calculator app up and do it. 

In short, as Bushwick Bill said, fuck school fuck teachers fuck homework!

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Guest

Guest

Posted
Posted (edited)

7 plus 8 is 5 in the ones column, 1 plus 4 plus 2 is 7 in the tens column.   75.

I could not help my kids with their fucked up math methods in school.  Then if I taught them my way, they got obliterated on class work.

Generally speaking, I do math way the fuck faster than most people in their heads.

Edited by slorch
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Mole

Mole 4333

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Posted

Without any real thinking about arithmetic, it's clearly a number greater than 70 and less than 80. In my own day-to-day life, I can't think of a scenario where anything in the range of 71-79 is a meaningful distinction, so I say it's somewhere in the 70s and move on. Meaningless precision is overrated. 

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Prepuce of Doom

Prepuce of Doom 21106

Posted
Posted
2 hours ago, Mole said:

Without any real thinking about arithmetic, it's clearly a number greater than 70 and less than 80. In my own day-to-day life, I can't think of a scenario where anything in the range of 71-79 is a meaningful distinction, so I say it's somewhere in the 70s and move on. Meaningless precision is overrated. 

Sounds like something that a mole would say. 

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Tom

Tom 2959

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Posted

What happens in my brain:

 

What's 47+28?  Okay.  47.....57....67....what was the other number? Shit...I need to check...oh yeah, it was 28.  Okay, so 47....57....67 plus 8...why does my stomach keep growling?  Have I not eaten?  What am I going to get for lunch today?  Probably tacos.  I need to sneak out of here soon.  Wait...what am I doing?  Okay, concentrate.  Let's see...47....I mean 67 plus 8 is...75?  Yes, 75.

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mininghorn88

mininghorn88 2298

Posted
Posted

47+28. I looked at it. 8+7 =15. Keep the 5 and carry the 1. 1+4+2=7. Put them together and you get 75.

Then I read the topic title again. Wait, what? Is this a trick question? Does it not equal 75? I do the math in my head again, yep, 75. What am I missing? Then I read the thread and see the different methods. How can something so simple be so complicated?!!

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SilasCoade

SilasCoade 2622

Posted
Posted
34 minutes ago, mininghorn88 said:

47+28. I looked at it. 8+7 =15. Keep the 5 and carry the 1. 1+4+2=7. Put them together and you get 75.

Then I read the topic title again. Wait, what? Is this a trick question? Does it not equal 75? I do the math in my head again, yep, 75. What am I missing? Then I read the thread and see the different methods. How can something so simple be so complicated?!!

I've thought too much about this.

There are really only two approaches.

Those that internalize the distributive property of addition: (x + y) + (a + b) === (x + a) + (y + b). In this case, (40 + 7) + (20 + 8)===(40 + 20) + (7 + 8).  This is recursive because the next step is 60 + 15 === (60 + 10) + (0 + 5) === 70 + 5 === 75.

Carrying the one is just a different formatting of the same principle with the application of an unnecessary sequence rule that state you must do the y+b portion first to get c and if c > 10 convert c === (10 + d). You then have to do x + a + 10 + d. Carrying the one is how I was  taught to do it but it is slower.

The other approach is to use the additive inverse: x + y === (x + z) + (y - z).

This approach is useful when certain numbers seem "easier" to add, such as multiples of five or ten. In this case one can see that adding something to 50 seems easier than adding it to 47, so you do (47 + 3) + (28 - 3) === 50 + 25. Of course you then have to do the other approach to get the final answer.

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Posted
Posted
19 minutes ago, Llogg said:

I've thought too much about this.

There are really only two approaches.

Those that internalize the distributive property of addition: (x + y) + (a + b) === (x + a) + (y + b). In this case, (40 + 7) + (20 + 8)===(40 + 20) + (7 + 8).  This is recursive because the next step is 60 + 15 === (60 + 10) + (0 + 5) === 70 + 5 === 75.

Carrying the one is just a different formatting of the same principle with the application of an unnecessary sequence rule that state you must do the y+b portion first to get c and if c > 10 convert c === (10 + d). You then have to do x + a + 10 + d. Carrying the one is how I was  taught to do it but it is slower.

The other approach is to use the additive inverse: x + y === (x + z) + (y - z).

This approach is useful when certain numbers seem "easier" to add, such as multiples of five or ten. In this case one can see that adding something to 50 seems easier than adding it to 47, so you do (47 + 3) + (28 - 3) === 50 + 25. Of course you then have to do the other approach to get the final answer.

proof?

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SilasCoade

SilasCoade 2622

Posted
Posted
1 hour ago, slorch said:

the quicker method.  Either way, it's two very simple equations combined.

Are you asking me to prove that it is quicker to do the explicit distributive property method over the carrying method? I mean, that's not something that there's going to have been a randomized controlled trial for but 1) it's quicker "for me", and 2) it is fewer logical steps when presented visually. Reading left to right the carry method requires these steps:

  1. read and ignore the tens place
  2. read the ones place and store it
  3. read and ignore the next tens place
  4. read and store the next ones place
  5. add the stored ones
  6. determine if the sum is greater than 10, if so store sum modulo 10 as the end or your ultimate sum and store sum divided by 10 separately as the carry digit
  7. read the tens place and store it
  8. read the next tens place and store it
  9. sum the tens place plus the carry digit
  10. prepend that sum to the result of step 6

The distributive method requires this

  1. read and store tens place
  2. read and store ones place
  3. read and store next tens place
  4. read and store next ones place
  5. sum tens places
  6. sum ones places
  7. sum steps 6 and 7

Note that if you're storing the tens digits the first time you read them and think you're doing the carry method, you're just implicitly doing the distributive method without realizing it.

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SilasCoade

SilasCoade 2622

Posted
Posted
2 minutes ago, slorch said:

Meh.  bullshit.

7+8 is 1(5)

1+4+2 is 7

75

Proving again that you're one of the stupider people on this board. You don't even realize the steps you took to get those 3 lines. Just because they happen quickly doesn't mean they don't happen.

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Posted
Posted (edited)
1 minute ago, Llogg said:

Proving again that you're one of the stupider people on this board. You don't even realize the steps you took to get those 3 lines. Just because they happen quickly doesn't mean they don't happen.

and just because you overexplain the living fuck out of simple concepts, doesn't make them more complicated.

 

any time you want to go IQ test or general knowledge, let's go, fuckboy...

 

 

Edited by slorch
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SilasCoade

SilasCoade 2622

Posted
Posted (edited)
5 minutes ago, slorch said:

and just because you overexplain the living fuck out of simple concepts, doesn't make them more complicated.

 

 

I never said it was complicated. If it seemed complicated to you that's telling, isn't it.

 

Tell you what, write a computer program that takes the text "47 + 28" and returns the integer sum 75. You cannot use any built-in string parsing functions that do the work for you. It's a really good way to figure out what your mind is actually doing even if you don't recognize it.

Edited by Llogg
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RPM

RPM 26360

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Posted

I've made fun of this all thread, but if I may digress... Back in ye olde days we were taught to add from the right and carry. That's how my brain was wired and remains so. Anyone thinking differently is a got dam red.

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clapclapclap

clapclapclap 9000

Posted
Posted
On 5/6/2021 at 11:24 AM, Degenerate Gardner said:

Add 2, subtract 2 to wash. 30+45=75.

 

On 5/6/2021 at 11:40 AM, Red Five said:

Add 30 to 47 then subtract 2. 

Bingo.  

You hear 47 first, but it's the +28 that tells you what is required.  Why then backtrack to start with 47 or some other method?  Adjust the last thing you heard (28 to 30) then back up to adjust the 47.  Efficient.

 

On 5/5/2021 at 11:48 PM, markstanco said:

77-2

"Progress!" - aggy

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