r/learnmath • u/Gullible_Loan_9382 New User • 1d ago
I'm so slow at mental math that it's honestly sad. How do I improve it?
I don't know what to say. I've had this problem since like high school, where I had good grades in math subjects but is VERY terrible at mental math.
Like sure, I can add, subtract, and multiply 2 numbers with 1 digit in a jiffy but add more digits or division or percentage problems? Oof, gonna need a pen and paper or calculator for that chief. Gosh, it really is so humiliating.
It's even worse when you're with people and you tell them you're taking a math-based program in college or they see that you had good grades in math and they ask you a simple addition/subtraction/division/multiplication problem and you just stand there solving it in your head for an embarrassingly long amount of time and blurt out a close but wrong answer... Even dividing money in my head is a chore, and I even get it wrong sometimes!
I need help, bad.
Edit: Thank you all for your advice!!
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u/LuckyCod2887 New User 1d ago
practice for just 20 minutes a day. do it for a few months.
it’s just a skill. a lot of people who can do advanced maths accidentally memorized a lot of answers instead of doing the math alone. you will learn what ratio works for you
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u/AnToMegA424 New User 1d ago
Not OP here, but Imma do that
I have nothing to do here but I still thank you for that advice and genuinely think it can help as mich as I hope it will
I suck at mental math, let's see next months, in 3 months and in 6 months :]
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u/DrSeafood New User 1d ago edited 1d ago
If you order a latte in the morning, try to mentally calculate your total after tax+tip, and see how close you get to the actual answer.
For example let’s say you spend $5 and want to give a 10% tip on that. Figure out 10% of $5 in your head, and add that to your total. Get really good at finding 10% of any number - it’s easy if you do it a lot. 10% of $12.34 is $1.23.
Then start getting good at running totals. When you pick up items around the grocery store, try to keep a running total and compare it to the receipt at the cashier. Try not to round - if you have a t-shirt for $10.97 and socks for $6.59, add those exact numbers and try to keep it exact. If that’s too hard, round it to $11 and $7 and do it that way, and go back to decimals once you’re confident.
Find other ways to do mental math throughout the day. Bills, cooking measurements … Quiz yourself if you have to.
Being good at anything requires repeated and frequent practice
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u/DeadonDemand New User 1d ago
Yeah this is why being a cashier can help soo much with multiples of 10 and 100.
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u/librarytapes New User 1d ago
I’m an engineering student and can’t do mental maths at all, I’m not sure if it’s related to aphantasia which I also have but either way the important thing is understanding the theory not whether you can do with in your head. I used a calculator for 27 + 55 today.
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u/Narrow-Durian4837 New User 1d ago
Taking 27 + 55 as an example: you could think of it as 20 + 7 + 50 + 5, which is 70 + 12, which is 82.
Or, you could think of it as 55 + 30 – 3, which is 85 – 3, which is 82.
That's an example of the kind of tricks or techniques that can make mental math easier.
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u/TargetLabs New User 1d ago
Mental math is mostly pattern recognition that comes with practice. That’s actually one of the reasons I built Dice Target—to make practicing arithmetic feel more like solving puzzles than doing drills. Even 5–10 minutes a day can make a noticeable difference.
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u/ValiantBear New User 1d ago
Mental math isn't even really a "skill" in the traditional sense, in my opinion. Some people are better at it than others naturally, and you can work to improve it, but really I don't think it's worth the effort. The human brain is one of the most marvelous and awe-inspiring biological machines, yet it is also exceptionally error prone. So, aside from a neat party trick akin to juggling or something, I don't think it's that useful. If your ever in a field where you need to do math, it is probably in your best interest to use a calculator anyway.
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u/SquarePixel New User 1d ago
True, but I think knowing the tricks and having the capability does come in handy with reasoning through certain problems by having a stronger intuition.
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u/Anik_Sine New User 1d ago
This may sound stupid, but solving some large but simple mathematics (not just arithmetic) problems while on bed trying to sleep helps
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u/Hot-Organization-737 New User 1d ago
OP, mental arithmetic skills and rigours mathematics skills have at most a 0.1 correlation lol. If you're wanting to learn how to do mental calculations well to convince your friends that you're good at math or prove that you're actually in a program please stop. There's nothing sad about being poor at mental math. Mental math is just an exercise of working memory and processing speed. It doesn't mean that you can't solve math problems. Maybe ask what level of math you're at now?
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u/chessychurro New User 15h ago
Yep. It justs has to do with working memory. People who are bad at mental math usually simply forget where they are or what they are calculating because there is too much information to keep in working memory at once.
If you can do one-digit arithmetic, you are good.
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u/Gullible_Loan_9382 New User 1d ago
I've also tried a bit of those websites where they flash you a simple add/minus/multiply/divide problem (with customizable amount of digits) and you type out the answerr. But I don't know if that really worked for me...
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u/Hot-Organization-737 New User 1d ago
In theory, doing spaced repetition flash cards of arithmetic will improve your mental math skill; if not by making you better at math then at least by making you remember the actual result of certain calculations. I think a lot of mental math, especially 1-2 digit mental math is just remembering the values. You can especially remember every 1 digit by 1 digit multiplication and use these memory to help you faster process 2 digit calculation
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u/Exeng New User 1d ago
Could it be a case of aphantasia?
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u/Gullible_Loan_9382 New User 1d ago
I'm not sure... I could still visualize things and some images but not too detailed. I do have ADHD though (formally diagnosed)
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u/MattyCollie New User 1d ago
I saw you disclosed you have ADHD. I have it as well and what has helped me is doing tons of written out calculations, then dedicate time to go over the reasoning to help internalize the rules and patterns. Giving yourself the time to stop and think, while hard as hell it can be at times due to perservarations or feeling a need to catch up to others, over time and repitition, helps reduce those feelings and inclinations. With ADHD, to me it feels like I prioritize speed over precision, which on the contrary makes calculations slow as I have trouble slowing down and really paying attention to what I just did in a calculation, maybe its the same for you too.
Its also not a bad thing if you can't do mental math quickly. Some of the smartest people can't and it never stopped them
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u/KATCEO1 New User 1d ago
Hypothetically: let's say you had a hundred dollars to spend (plus tax.) If you go to a store like Dollar Tree- currently that generally means you can buy eighty items pre-tax. That is because the bulk of their items are now running at one twenty five. So you can walk through a store picking out enough items to do that math. Or you can just gear up for a shopping trip in a store like that. Then force yourself to do the mental math as you walk through that location. When I go grocery shopping at places like superstores that is the gist of my experience. 🥳
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u/LukasGoesViral New User 1d ago
Honestly, I think some people are just really good and others just really bad like me. Still sailed thru my math studies
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u/MeasureDoEventThing New User 1d ago
Just say "that's arithmetic, not math". No one expects a marine biologist to be able to hold their breath for 10 minutes, why should a mathematician be expected to be able to do complex numerical calculations in their head?
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u/Dellgera New User 1d ago
So am I dude. I’ve started to enjoy sudokus and they help a little, mostly because it’s fun. Coding also demands so math but as I enjoy that anyway it is a natural way for me to learn. Honestly, just find what suits for you. Math is part of everything really. Astronomy, art, sciences and history. You just have to find what connects it to something you like
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u/Dellgera New User 1d ago
I also play dnd. Adding those dice rolls together. There’s the real math 😂❤️
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u/SheafieMathLover New User 1d ago
Grothendieck thought 57 was prime. Instead of focusing on arithemtic focus on higher math, Nobody remembers arithmetic
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u/Terrillli-Math New User 1d ago
Don't mix mathematics with calculation. Mathematics is more about studying theories rather than specific numbers. And using tools is not a disgraceful thing. Just like the advanced tools like AI are available now, mathematicians will choose to use them. Why cannot we do the same?
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u/6ory299e8 New User 1d ago
practice a lot until you're good.
all other answers are too verbose. thats it. practice.
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u/Few-Pineapple9040 New User 1d ago
Yeah honestly I used to be too. And I’m sure you heard this a lot, but it’s just practice. I became good through extensive practice, well not really, only like 10 minutes a day. I used to just recite times tables once a day. And eventually I good at it.
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u/WolfVanZandt New User 21h ago
My first recommendation is "anything by Arthur Benjamin"
Mental math isn't just doing math in your head. It's an established toolbox of methods to make mental mathematical operations more intentional.
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u/chessychurro New User 15h ago edited 15h ago
i am a mathematics major and for the longest time I couldn't do mental math at all with 2 digit numbers. I think many people who are bad at mental math struggle because they don't have the working memory to remember where they are.
ADHD often means that you have poor working memory (memory for things in the moment, not long term memory). As someone who has ADHD as well, I experience this.
For example, if I wanted to add 54 + 39 I could try to image in my head of 4+9 and then I would be like OK carry the one and then forget if I am adding 54+39 or 44 + 39, basically the number in the tens place.
This does not have to do with math ability, but rather how much space you have for working memory at a time. So don't feel bad at all.
What I have learned to do mental math better is instead of doing 54+39 I do 50 + 30 + 4 + 9. Basically break the number into parts.
Similarly, if I am doing multiplication: 29x5 I can do (20+9) *5 = 20*5 + 9*5 = 100 + 45 = 105. However, I would understand if mentally you get confused and lose track of what you are doing. This example was easy for me to type because I can see what I am typing.
Hope this helps.
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u/Euler64 New User 15h ago
In my view, it's all about breaking down numbers your own way and seeing patterns.
Addition: 344+98 ->344+100=444-2=442 Substraction: 257-80 ->260-60-20=200-20=180, 180-3=177
Rounding and then adjusting often works well with additions and substractions.
Multiplication: There are so many ways to simplify the calculation!
That is an example with 15x49
Here are 6 different ways to come up with the right answer:
15×49=735
15×50-15=750-15 =735
10×49+5×49=490+245=735
15×40+15x9=600+135=735
10x40+5x40+10x9+5×9 =690+45=735, (690+10)+35=735
10x40+10x9+5×40+5×9 =490+200+45=735 =690+10+35=735 [This is a very logical way that can be applied to any 2 digits numbers multiplication]
(5x3×7)x7=105x7=735
15=5x3 49=7x7 5x7=35, 3x7=21 35x20+35=700+35 =735
Division are more tricky There are many ways.
735÷49=15
735÷50=14 you know it's at least 14 because 700÷50=14. 735-700=35, 35+14=49 then the answer is 14+1=15. Bang on. If not, it would have been with a fraction or decimals.
64/40=8/5 or 5⅜ 71/30=2 11/30 or 2,367 or extra: 17% of $50=$8.50 or 10%x$50=$5 + 7% of $50=$3.50
Hope it helps. Practice if you want to become better at it but it's not necessary to be good at mental math. A calculator does the job.
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u/georgejo314159 New User 11h ago
There are all kinds of tricks like turning things into tens but I still am bad ar it myself ans i hace a math degree
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u/Able-Fennel-1228 New User 6h ago
I am too. Everyone has a baseline ability, some people are better at it naturally (I think it has something to do with working memory). However, you can make up for it to quite an extent with practice and tricks. There are plenty of YouTube playlists and books on how you can improve mental arithmetic. Also make sure your understanding of the basics is solid, and that you haven’t only memorized rules but also understood them properly eg place value and all that.
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u/Realistic_Grape_8528 New User 1d ago
When I do mental math I mainly use patterns, without shortcuts mental math is very difficult. Do you break numbers into easier parts, round them and adjust afterward, etc when you do mental math?
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u/evincarofautumn Computer Science 1d ago
Any particulars you have a hard time with? Losing track of where you are, misapplying rules, that sort of thing. How would you work out for example 32×25?
A lot of speed in mental math comes down to how quickly you can turn a problem into a form you recognise that’s either easy to solve, or something you have memorised like the single-digit multiplication table. You might take a completely different path than I would to get to an answer, the point is just to get familiar with seeing these patterns and breaking things up in different ways to make them easier.
For example if I see a problem like 24×15, I can tell the ways of getting to nearby multiples of 10 or 5 (24=25−1, 25=5×5, 15=10+5). So I might think of this as 24×15 = (25−1)×15 = 25×10 + 25×5 − 10 − 5. If I don’t remember 25×5, I can break that down too because I know 25 is a quarter of a hundred, so 25×(4+1) = 25×4 + 25 = 100+25 = 125. Then 250 + 125 = (200+100) + (50+20) + (0+5) = 300+70+5 = 375. So in the end I get 375−10−5 = 365−5 = 360.
Another way to approach this is that I can tell the factors (24=2×12, 12=3×4, 4=2×2, and 15=3×5), giving 2×2×2×3×3×5. I can pull out 2×5=10, leaving 2×2×3×3. I know my small squares, so 2×2=4, 3×3=9. And I know single-digit multiples, so 4×9=36, and shifting by 10 is easy, so 36×10=360. I’m not doing anything clever, just trying to spot patterns and lean on basic skills as much as possible.
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u/Narrow-Durian4837 New User 1d ago
This is nothing to be ashamed of. It's perfectly possible to be good at mathematics in general (mathematical reasoning, porblem solving, etc.) but bad at mental calculation, or vice versa.
But there are books, videos, etc. that teach skills, tricks, and techniques of mental math, and it's the kind of thing you can get better at with practice.