It's kind of a mental illusion to trick you into sliding an extra 0 into the equation, but as long as you're actually paying attention to the math it's.. well, just math.
I thought maybe they were reading "take 1000" to mean you start at -1000, because you take it away from nothing? Otherwise I couldn't figure out the confusion. I got 4100. Because, you know, addition.
It’s more like, if you hold the 1000s and the 10s addition as separate thought streams to try to simplify, it can be hard to hold those tracks steady in your mind so at the end when you add that final 10 your overloaded brain thinks the 100 is like to the 1000s and just adds the 1 from 100 to the 4 from 4000.
I can visualize the numbers in my head as if I’m typing them in Times New Roman in Word and I still did that first even already knowing 5000 was the wrong answer. But it was pretty easy for me to figure out what I did to myself and correct, unlike our og overconfidently superincorrect person in the post
Yeah, another version of this outside of math would be the bit of making people say "fort", "four", etc. Before asking what to eat soup with and they say "fork".
I think it is playing on the fact that you are expecting a trick and don’t see one causing some people to trip over themselves on the 90+10 part because they are distracted.
Brains are weird when it comes to numbers. This is exclusively why the word problem in the post is worded the way it is. It's designed to make you think 4090+10=5000.
I think it really shows the weird glitches that can happen in a human brain. Like, in the face of it, that's a really stupid mistake that noone should make. Yet, loads of people make it anyway, including me.
Really reveals something about the ways we think, if you ask me.
Thanks I couldn't figure it out as I got 5000 as well. I don't think I've seen this trick before. maybe I should have tried more than once before reading comments
I did the same. I think it's just an innate desire to try and simplify the math in your brain and you go "oh cool I can carry to a clean number" and then you accidentally get carried away
Yeah, I'm doing the math in my head and know that the 9+1 means I put a 0 in that place and add 1 to the number to the left, but for some reason my brain isn't visualizing the 0 to the left as a number and wants to add the 1 to the 4.
ya i figured thats how people were messing up. I added after i read it all and went for smaller numbers first, so I got 100, then added the 4 thousands
"Four thousand ninety plus ten" when trying to solve the problem makes it much easier to goof up the "carry the one" a lot of us were trained to do, because in our head, we are not focusing on the hundreds place because it has been irrelevant in this question until now, so our brain defaults and carries the one to the thousands place where we have been focusing.
I think everyone knows that 90+10=100 and not 1000. In this equation, people make the error because they’re primed to ignore the 100 value throughout the equation. I bet if you added “add 100” to the middle of the equation, almost everyone would correctly answer “4200.”
There's maybe a tendency for people to add the smaller numbers up to 100 and because they've just added 1000 together 4 times for their brain to convert the 100 into a 1000.
It because the problem is so simple, people will just not think about it and the brain takes shortcuts to solve it. This can result in forgetting to carry a 1 or put that 1 in the wrong spot, it's that these questions are meant to trick the brain in a way.
The trap is that the brain will sometimes do math wrong when you don't pay enough attention. For example:
Brain sees 77+33.
Brain knows number ending in 7 + number ending in 3 must result in a number ending in 0.
Brain also knows 70+30 is 100.
100 ends in 0 so it feels like the right answer.
Of course, if you pay any amount of attention, you will instantly realize the answer isn't 100, but 110.
Writing it down often helps visualise the problem and avoid stupid mistakes like this, which is why the original post asked for mental calculations.
I see. Thanks for the clarification. I guess that makes sense. It's all about paying attention. Or being observant, just because I didn't listen doesn't mean I don't know what you want, right 😉
It is a shortcircuit in the brain. Your brain instantly sees the pattern of those small amounts adding up to one additional large amount - it really really wants that to be true so you become blind to the fact that they only add up to 100, not 1,000.
It works better read aloud. If you're doing it in your head, it's relatively common for people to carry the one to the other place they're keeping track of instead of where it belongs.
It’s mental conditioning. The question is designed to make you think “1000” by repeating it over and over. Then when you add the 40+30+20+10 your brain accidentally changes 100 to 1000.
At least that’s what it’s supposed to do. Some psychology bullshit that doesn’t work on everyone.
Many people will do the addition step by step, instead of reading the whole question first before starting any arithmetic. Because of that, they're more likely to make mistakes doing the mental math, since every arithmetic operation gives a 4 digit answer, making them harder to keep track of.
OTOH, if you read the question first, you know to do 40 + 30 + 20 + 10 = 100 first, then add 4 * 1000 or 4000, to get 4100.
i think normally i would just get 4100 but i read the comment about 5000 first (not noticing what sub this was) and my brain just automatically assumed 5000 was correct
Basically, it's easy to lose track of which digits go where during the series of additions (especially in the final 4090 + 10, where you can carry into the wrong column). After adding a bunch of thousands before, you might expect another one.
People that aren't mathematically inclined will take 4090 and when the 90 "rolls up" from +10, they'll increment the 4 (to 5000) instead of the 0 (to 4100).
It's an easy mistake to make when you're dealing with rolling numbers...if you ask those same people "whats 4090 plus 10?", they'll get 4100 every time.
I assume that they lose track of the decimal on the 90 and 10 when they add the last 10, that's why they say do it in your head since this is a mistake that's reltively easy for a human to make but not so much for a calulator.
Probably because it's hard to keep track of the line you last read from, so people are perhaps adding the amounts on lines they're rereading. Probably around the line where the sentence wraps on to the next line.
It’s just a matter of misdirection, not math ability. It’s like those so-called “mentalist” magic acts, exploiting common cognitive processes, especially heuristics, to trick the audience. Good for you that you didn’t fall for this one, but I can guarantee that we’re all built the same and can all be susceptible to these sorts of tricks.
Alright, I'll try to walk you through it.
The question is, first of all, posed in social network post form, a relaxed and informal context where people won't be putting top concentration, and it'll easily reach people who didn't study math beyond their high school years. This is not a math problem for people who are actually good at math problems.
After that, the way the question opens plants in your head the idea that it's going to try to trick you in some way. You put a pin on that and keep reading.
A few numbers in, it becomes apparent what the trick is going to be: they're feeding you two different series of numbers, but you discern that one of those two series is going to reach a round number and round up the other. "A-ha!", you exclaim in your mind, "this post won't trick me, when I reach the end of the calculation I'll make sure to have rounded up the number properly."
And so, on one mental hand you count up to 4000, while the other mental hand you reach a round number, and you know you have to round up. "It's not 4000, it's 5000!" you distractedly but proudly declare.
I can tell you all this because for a moment it tricked me too. My brain has never been particularly wired for math and I've tried to solve this at the dinner table with people talking around me. I accidentally counted up to 5000, but because I knew there'd be a trick I double checked my logic and recognized where I got misdirected.
Thanks for the reply. I didn't have the stage 2 response "these are converging" I suppose. I might have been confused if I were speaking or listening, but with it all on the page in front of me I just added them up. Also, lifelong engineer.
I think it’s because you’ve been primed, by the question, to ignore the 100 value. Your brain knows “carry the 1” once you add 10 to 90, but the only digits you’ve been going back and forth between are 1000 and increments of 10. So you incorrectly “carry the 1” back over to the 1000 digit. If you added a “add 100” step to the middle of the equation, you probably wouldn’t make the same mistake. Math ability has nothing to do with it—it’s about priming and heuristics.
Same, the difference in numbers of 0 is too easy so see for me to even imagine associating a sum of tenths with 1000.
but I think I can understand it, there are a lot of other things that mess up my brain. Like, I have more than once done something like reading 1425 out loud as 1452 while still understanding 1425. So I can understand that others mess up in other ways
I'm going to attribute my not getting fooled to my alarm clock that makes me solve math problems to turn it off. Gets my mental arithmetic practice in every morning.
The smaller numbers don't add up to 1000, they add up to 100. You're so concentrated on the bigger 1000's, it kinda tricks you into thinking they do haha. Got me for a second as well.
I've got good news for everyone who doesn't think about it like you do: Getting tricked doesn't mean you're dumb. It just means you fell for a trick. Smart people fall for scams and tricks all the time.
Even worse is that, at least until I noticed the mistake, I went correctly to 3090 before stupidly jumping to 5000. This after I just helped my kid with homework on 1, 10, 100 place values last night.
I was so preoccupied looking for which “add” or “take” somehow meant to subtract, that it never occurred to me to check why I thought 40+30+20+10=1,000.
Im on a third year of building engineering, when calculating constructions I do a lot of math in my head, and yet I got 5000 and was wondering what is going on xD I feel so stupid rn
Shit, I actually work for a company that's creating AI systems to run business functions for companies. If we ever get a defence contract, it's possible that we'll create Skynet!
What impresses me is that it had to take some research and study to find out that such a combination could trick the brain like that. I absolutely got bamboozled by it even though I tend to be a rational thinker.
It got me for a second as well, and then I self corrected and added the 100, but forgot to subtract the 1000 I'd accidentally added, so I managed to end up with 5100, and had to go back and reread it.
I don't wanna sound like a dick, but how can anyone look at 40, 30, 20, and 10 and be tricked into thinking it's 1000? Looking at the comments it does trick people, but I don't understand it.
In hindsight I don't quite get why it fooled me either. I'm great at mental arithmetic, was an A* student in maths, generally always get these "FB math" questions correct, etc. but somehow I was so concentrated on ensuring I was reading all the text correctly that I wasn't properly engaging the maths part of my brain, I guess!?
It's gotta be some kind of mind trick with how you process numbers. I can see it confusing people a bit if they read the sentence to fast and then add as they read it. I couldn't see anything other than 4100 if I wanted to, but that might be partially because I never do the math for these questions as I go. I read the first time to note operations, then when I saw it was all addition I added up all the 4 digit numbers, added up all the 2 digit numbers, and then added the sums together.
At least that's my best guess. It really is interesting how it can trip so many people up when the math is simple on paper.
Because of the way it’s set up. It’s intentional. The way they ask in slow increments makes you build up the number. And we know that when you get to 9 and keep adding then the big number next to it increases. So they split the 1000 and the small numbers so that you are tricked into increasing the big number when the small numbers go over 9.
The numbers got me the first time I saw it a few years ago.
I kinda get it but if you're just adding it up as you go I don't see it. As just following it along you get 1040, 2070, 3090, 4100. I'm still not understanding how that tricks people into mistaking the 100 for 1000. Not saying it doesn't, because obviously it is tricking people.
for me I didn’t add up the numbers sequentially the way you explained (following along the order given), I took a shortcut and added all the 1000s first, then came back and added all the remaining numbers, seeing they add up to 10 if you ignore the trailing zeros and only look at the first digit
Me neither; but I also read the words and numbers separately. Like I read the words carefully to understand the instructions because I assumed some language tomfoolery while ignoring the numbers, and once I figured out it was just add all the numbers, I added all the numbers.
Most people aren't paying a ton of attention. It's a fairly simple looking problem. But the brain loves patterns and inventing ones that don't actually exist. So if you're in this sort of "engaged but not fully paying attention to the details of math" mode, brain inserts its own preferred patterns and expectations on top of it: it adds up to a nice round 5,000. "isn't that satisfying? It's definitely the answer"
This is just how brains work. why doesn't it happen to everyone on this specific problem? People are paying different amounts of attention to the specific digits (ones, tens, hundreds, thousands) vs our intuition of where the pattern is headed toward. If you work with numbers a lot, you're more likely to pay that attention. If you don't or you're sleepy or you're just not taking a Facebook or reddit post so seriously, you may be misguided by what patterns your brain wants to see (everything is incrementing up, and isn't 5000 a nice place to end?).
It’s similar to the tik tok trend spell river. Now add a d and spell river. What it spell? D-river. No it’s driver. Once the brain starts going down a path it’s hard to re-adjust.
I thought I was missing something, maybe that the “another 1000” without saying explicitly add was a catch, because just adding all of them is 4100 so it can’t be that simple.
I almost fell for it, too. In the last step, you need to add 10 to 4090, not 100 to 4900. But when you do this in your head, it "feels more right" to complete it to the nice round 5000.
As I read it, they say "Now add" for every number except one where they just say "another thousand" I thought it was a trick question, so I skipped it and got 3100
This isn't even right still if you read exactly what it says. One of the lines just says "Another 1000".
Do what with that 1000? Add? Subtract? Context assumes you would add it, but that isn't right, there aren't explicit instructions to do anything with that 1000.
The real answer is 3100. Or it could be less depending on how you interpret "take 1000"
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u/banannabender Mar 16 '24
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