I'm really curious to see how other DIY investors and landlords answer this mental addition question versus the general population.

Um, Jim, not gonna lie, weirdest question I have ever seen in a RE forum. :-)

I add 7 then 20. 

I shift 2 from 27 to 48, then add 25 and 50 to get 75. 

I had the 20 to 48 and then I add the 7 to 68 to get 75. 

Hopefully this will shed light as to why I turn into a werewolf during full moons and run around howling looking for value-add real estate deals. 

I also shift 2 to 48 to get 50, then just add 50 and 25.

My mind adds the 4 and the 2 plus the carry over.

I'm in the minority so far, but I add 40 plus 20, then add the 15. I am waiting for the reply of "full on panic!!!!"

Originally posted by @Jill F. :
(40+20) 60+ (8+7) 15 =75

Same for me!

@Jim K. Take 2 from 27 to make the 48 50, then 50 plus 25 is 75 is how I would do in my head, or would do 8 plus 7 is 15, carry the 1, 4 plus 2 plus 1 is 7 - also 75.... quickly do both ways in my head to check my work :)

Thanks so much for responding. I saw this question elsewhere. The standard "math person" way seems to be what @Russell Brazil and @Dawn P. do. @Jill F. does it the way it was taught to me in my NY primary and secondary school experiences. @Mike Dymski  and @Matt Groth  take what I see as the European approach to carrying over (guys, it may just be how basic math was done in your state or local curriculums, IDK).

@Karl B. and @David Lee Hall, III both use the same basic mental math shortcut approach.

But here's the thing, guys -- I cannot help but look at that and see 48 hours as two days and 27 as one day (24 hours) plus three hours. So I do 48 + 24 = 72 (three days), then add 3. It just seems inconceivable to me that people would do it mentally any other way. And I'm not saying my way is better, I'm wondering why it works that way for me.

Originally posted by @Jim K.
I cannot help but look at that and see 48 hours as two days and 27 as one day (24 hours) plus three hours. So I do 48 + 24 = 72 (three days), then add 3... I'm wondering why it works that way for me.

I think you would want to see why you turn the numbers into days. Did you used to ever be on a very regimented schedule (military maybe)? If you can identify that, you may know why you do it with simple addition. I could see if you always moved cases of a product as a supplier for 30 years, that you would do mental math in “cases” as it would be natural to you (a case could be 20, 24, 30, etc.).

Originally posted by @Jim K. :

I'm really curious to see how other DIY investors and landlords answer this mental addition question versus the general population.

40+20=60

8+8=16

16-1=15

15+60=75

(or I excel it).

@David Lee Hall, III

Not military, but it's probably linked to time management. I have renovation periods now where I have to manage my time very well, and structured time management was a regular part of my life for quite a few years as a teacher. But it's weird as hell to see the outcomes like this.

@Jim K. I take 2 from 27, to make 48= 50 and whala adding 25 is easy peasy to get to 75🧐

@Scott Mac

Thank you, Scott. That's the second shortcut approach I saw elsewhere -- and predictably, from an experienced finance guy.

Originally posted by @Jill L Ripley :

@Jim K. I take 2 from 27, to make 48= 50 and whala adding 25 is easy peasy to get to 75🧐

Yes, that's the good-at-math mental shortcut approach. This is why my right hand's fingers are so crooked and I'm just glad I'm not missing any of them.

@Jim K. 😂

I also add 60 and 15

Using the INSANE NEW math my grandsons public school enforced he would have had to decompose the numbers AND show his work or get a zero regardless of the solution.

        48      +     27    =

      /     \         / \

  40          8   20       7

        40    +    20    =  60

           8    +      7   =  15

          60  +   15  = 85

His public school went 'covid-hybrid-zoom', so now we send him to a private school where they teach him how to solve MATH the way we did in the dark ages. His has since excelled in math, reading & ALL aspects of elementary ed. Then again the class size is 8 not 35.

I turn 48 into 50 and 27 into 30 and get 80 then take the 5 I added in the beginning away and get 75

I think " 4' plus 2' 3" = 6' 3" (six feet, three inches)

I reach for my phone and hit the calculator app

@Tim Hager same for me.

Ask them about multiplying those numbers in their head for fun :)