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Featured Replies

Been seeing this go around the webs.

8 + 7 = 5. 4 +2 +1 = 7.  For a total of 75. 

 

See 47 and 28

Subtract 3 from 28 to make 25  and add 3 to 47 to make 50

50 + 25 = 75

  • Popular Post

i-was-told-there-would-be-no-math.jpg

Been seeing this go around the webs.
8 + 7 = 5. 4 +2 +1 = 7.  For a total of 75. 
 

That there is a thread you are the undisputed champ of that already addresses this.

Add 8 to 7 to get the ones digit (5), then add 2+1+4 to get the tens digit (7). I don't consciously go through that process -- two digit sums just sort of appear automatically for me -- but if I break down the process that's how it happens. 

45 minutes ago, Laxtonto said:

See 47 and 28

Subtract 3 from 28 to make 25  and add 3 to 47 to make 50

50 + 25 = 75

Add 3 to 47 to make 50, then take away 3 from 28 to make 25...

Funny. 

Edited by Prepuce of Doom

  • Popular Post

Is this a joke?

40+20=60
7+8=15
60+15=75

  • Popular Post

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.  

Interesting to see how differently some of y’all broke it down to arrive at the same answer. 

1 hour ago, woohorn said:

Is this a joke?

40+20=60
7+8=15
60+15=75

No it isn't a joke and that isn't the fastest or most accurate way of doing it if you're actually good at mental math. 

Even though Vic phrased the numbers in reverse. 

But what ChiTown said is what I do. Take the singles off the 2nd number - add the tens - then add the singles.

If I'm looking at 28 + 47 I do 8 plus 47 is 55 plus 20 is 75. 

If I'm looking at 47 + 28 I do 47 plus 20 is 67 plus 8 is 75. 

YMMV.

 

Edited by ztejas

6 hours ago, ztejas said:

No it isn't a joke and that isn't the fastest or most accurate way of doing it if you're actually good at mental math. 

Even though Vic phrased the numbers in reverse. 

But what ChiTown said is what I do. Take the singles off the 2nd number - add the tens - then add the singles.

If I'm looking at 28 + 47 I do 8 plus 47 is 55 plus 20 is 75. 

If I'm looking at 47 + 28 I do 47 plus 20 is 67 plus 8 is 75. 

YMMV.

 

Is someone timing how long each method takes?  It may take someone longer to do the "fastest" method, depending on how their brain works.  And how is one method more accurate than another if they all produce the correct answer 100% of the time?

I personally dump 28 and 47 toothpicks on the floor and then count them all Rainman style. 

 

Edited by idigTexas
OU sucks

8 hours ago, Llogg said:

40+20+7+8

Mostly this but I pretty much see 60 + 15 even though 40+20 and 7+8 is also processing.

4+2=6, see that I'm going to carry the next operation so make it a 7, then I've already done the 8+7 so tack on the 5.

I didn't really know that I did that.

9 hours ago, woohorn said:

Is this a joke?

40+20=60
7+8=15
60+15=75

 

18 minutes ago, mdmost said:

7+8=15

40+20=60

15+60=75

These.  And I do basic arithmetic incredibly fast and accurately in my head, using that sort of methodology.  I use it in real-time, like cross-examining a witness on damages calculation, and I can usually spit out the next number before he can do it on a calculator.  

Nobody taught that, it's just a mental shortcut that I -- and obviously lots of other folks -- developed on their own.

Add the tens while peeking at the ones to see if I’ll be carrying a one.  Then get the last digit from the ones  

4 + 2 + (is there an extra +1? Yes. Then +1)  Tens place is 7  

8 + 7, last digit = 5, so ones place is 5. 

13 minutes ago, jeevsie said:

4+2=6, see that I'm going to carry the next operation so make it a 7, then I've already done the 8+7 so tack on the 5.

I didn't really know that I did that.

Ah. I see I basically wrote the same thing. 

19 minutes ago, Brisketexan said:

 

These.  And I do basic arithmetic incredibly fast and accurately in my head, using that sort of methodology.  I use it in real-time, like cross-examining a witness on damages calculation, and I can usually spit out the next number before he can do it on a calculator.  

Nobody taught that, it's just a mental shortcut that I -- and obviously lots of other folks -- developed on their own.

distributive property FTW

10 hours ago, Vic Mackey said:

Been seeing this go around the webs.

8 + 7 = 5. 4 +2 +1 = 7.  For a total of 75. 

 

Blink 182 Reaction GIF

20 +40

8+7

 

What is this horseshit you posted?

 

PS I know a guy that can multiply 3 digit numbers by 2 numbers in his head in 3-4 seconds . It is at the same time impressive and creepy 

Edited by Dennis Taylor

4+2=6, see that I'm going to carry the next operation so make it a 7, then I've already done the 8+7 so tack on the 5.
I didn't really know that I did that.

Same.
1 hour ago, Dennis Taylor said:

 

Blink 182 Reaction GIF

20 +40

8+7

 

What is this horseshit you posted?

 

PS I know a guy that can multiply 3 digit numbers by 2 numbers in his head in 3-4 seconds . It is at the same time impressive and creepy 

Craziest shit I’ve seen in all my years is a patient who could tell you what day of the week you were born based on birthday.  And it took him less than 2 seconds.  I brought in 30 different people to stump him.  Impossible.  Freaked me the fuck out.  

1 hour ago, Nolacycling said:

(47 + 20) + 8

 

My middle school students would need a calculator.  

This.  I wrote it out but this is the shortest,  best way.  Other than the memorizing guy, who is likely full of shit.  

Some of you make me wonder...
 

900447CC-0E12-4BED-B915-789A333330AD.gif

12 hours ago, honolulu horn said:

Add 8 to 7 to get the ones digit (5), then add 2+1+4 to get the tens digit (7). I don't consciously go through that process -- two digit sums just sort of appear automatically for me -- but if I break down the process that's how it happens. 

This is me as well.

1 hour ago, Nolacycling said:

(47 + 20) + 8

 

My middle school students would need a calculator.  

 

16 minutes ago, Red Five said:

Add 30 to 47 then subtract 2. 

These 2 are basically the same and pretty much both take zero time.  I’m admittedly fascinated by this type of shit...

What happens in my brain?

 

Where's the image.jpeg.fbb6793693095e584cc2e39dec715cbe.jpeghappens in my brain.

 

 

 

Seriously though 7+8=15 2+4 =6(omitting the 0's)  6 +`1=7  answer 75

 

 

 

13 hours ago, woohorn said:

Is this a joke?

40+20=60
7+8=15
60+15=75

this... starting to see why "new" math teaching was developed

14 hours ago, woohorn said:

Is this a joke?

40+20=60
7+8=15
60+15=75

I add 4+2, then 8+7, and move the 0 to the end in my head.

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