How good are you at small mental arithmetic tasks and other every day skills.

[MagnusTheBrewer]

I do estimation and conversions all day every day while doing three other things at the same time. When I get stuck converting volume to weight or vice versa, I know I'm having a bad day and time to take some happy pills.

 

[Xstatic1]

r3a11y g00d.

 

[Leros]

I'm pretty good at random small stuff. Its mostly simple little tricks. Like what DrPizza said but simpler.

15% of X = 10% of X + 0.5(10% of x)
9*x = 10x - x

Funny story. Just two weeks ago, a bouncer wouldn't let me in a bar because he thought I was underage when he looked at my license. Even worse, he spent about 5-10 seconds looking at before he decided I was underage. I had to walk him through the math to prove that I was actually my age.

 

[Dr. Detroit]

I'm really good at simple mental math including multiple levels of percentages.

I immediately break the problem down and then recalc and wallah!

Its useful at times.

 

[jm30]

Absolutely horrible. It's a little embarrassing, and I've been thinking about practicing a little with a book called "The Secrets of Mental Math," which looks decent. But it's pretty boring.

 

[DrPizza]

I'm pretty good at random small stuff. Its mostly simple little tricks. Like what DrPizza said but simpler.

15% of X = 10% of X + 0.5(10% of x)
9*x = 10x - x

Funny story. Just two weeks ago, a bouncer wouldn't let me in a bar because he thought I was underage when he looked at my license. Even worse, he spent about 5-10 seconds looking at before he decided I was underage. I had to walk him through the math to prove that I was actually my age.

When I was in college, the drinking age was 19. I was only 18. In general, bouncers are dumb. I handed him my actual ID. He held it up to a bright light to see if there were any changes, he held it up to a black like to look for changes, he looked at the picture & looked at me for about 10 seconds, "Ok, go ahead." Dumbass never checked the date.

 

[meltdown75]

i don't like to toot my own horn but i guess i'm fairly decent... i have to be in my line of work.

 

[PaperclipGod]

I was always fairly good at math in both HS and university (not bragging here I'm not talking anything really special) but simple things like this I've always had issues with for some reason. It's somewhat similar to by handicapped spelling and punctuation contrasted with my otherwise above average prose style (as others have critiqued me anyway).

I'm the opposite. Did horrible in math at school, but I can usually do simple math a lot faster than friends/family. Fast at converting between percentages/decimals/fractions, too. Ask me to calculate anything using concepts more advanced than 6th grade math, though, and it'll take me eons. :hmm:

 

[MotF Bane]

For addition or subtraction, very fast. Something like 220 + 380 is instantaneous, I just see it there. For multiplication, I'll have an estimate in a second, and then the real answer a few seconds later.

 

[MotF Bane]

If I had to multiply two simple 2-digit numbers like 37 and 43 together, I'd immediately recognize that 40 was in the middle of them. (40-3)(40+3)=1600-9 = 1591

How did you do that? -3*3=-9? But what if you were doing, say, 44*37?

 

[meltdown75]

my cpu is a neural-net processor... a learning computah

 

[PaperclipGod]

How did you do that? -3*3=-9? But what if you were doing, say, 44*37?

That's a cool trick. If he did 44*37, I'm thinking it'd be (40+4)(40-3)=1588? Too lazy to check if thats right, though.:awe:

 

[MotF Bane]

That's a cool trick. If he did 44*37, I'm thinking it'd be (40+4)(40-3)=1588? Too lazy to check if thats right, though.:awe:

1628. So no.

 

[Possessed Freak]

That's a cool trick. If he did 44*37, I'm thinking it'd be (40+4)(40-3)=1588? Too lazy to check if thats right, though.:awe:

(40-3)(40+3)=1600-9 = 1591

The way works because of the FOIL method. The inner pair (-3*40) = -120 the outer pair (40 *3) = 120. They cancel. You are left with the last pair being -9. First * Last = 1600 - 9.

For your example you have 40*40 + 40*-3 + 4*40 + 4*-3 = 1600 - 120 + 160 -12 = 1628.

[edit]Oh, I had to do long division on an exam back in college. (I forgot my 4 function calculator), I sat there trying to figure out what to do with the remainder for 5 minutes. Still figured it out to the nearest cent (accounting) and got an A. Professor was wondering why I had all my margins in the test filled with math though!

 

[blinblue]

How did you do that? -3*3=-9? But what if you were doing, say, 44*37?

One way to do that is to recognize that 44*37=37+(43*37), which is then 37+(40+3)(40-3)=37+1600-9=1628 (which is the answer).
Of course, shortcuts like that only work well if you notice them quickly.

I personally am not that great at mental math. I'm decent at estimating, but honestly, if I'm ever in a situation in which I need the correct answer, I'd much prefer to get it correct and use a calculator, then get it wrong in my head.

That said, when I was doing math is school, I was notorious for doing a bunch of the steps in my head (usually manipulation steps, not arithmetic steps). I actually am pretty good at it now.

My job right now involves testing math problems, sometimes its helpful to do things in my head, but most of the time it goes into Wolfram Alpha to make sure I'm doing it right.

 

[destrekor]

My mental RAM is low.

My intelligence is average or slightly above, and I have a very good imagination, but my short term mental capacity for large numbers and images is low.

Truth.

I don't know how many times I've looked at my watch, immediately understood what time it is (analog face), and then returned to whatever I was or wasn't doing (procrastination or not prepared for class yet, as example of the latter).

I shit you not, no more than 5 seconds may pass, and I'm like "WTF did my watch say?", look again, :hmm:, move on. Sometimes, another 5 seconds pass, and it happens again.
Rather comical. It's not missing the numbers, it's just my brain is odd. I can do the same with digital time, see the time, no processing involved, and then, wait what time was it?

Many things with numbers are that way for me. I'm great with basic arithmetic, into algebra, beyond algebra lies the math I loathe. Imaginary numbers? For reals? We teach this shit?!

Most things with numbers that I forget, it's because at the immediate time I visually recognized what it was, understood it on a recognition level, but it stopped there. I have to force myself to stare at it a little, and force my inner-brain to observe and remember.

 

[Zeeky Boogy Doog]

I'm faster than my friends at most mental math when restricted to add/sub/mult/div, one of which is a math major, but he's definitely capable of doing much more difficult math than I.

 

[Fenixgoon]

pretty bad now

most of the math i do is either symbolic or involves things too large to do mentally (ie, power series)

i'm still good at rough estimates of stuff though

 

[MotF Bane]

The way works because of the FOIL method. The inner pair (-3*40) = -120 the outer pair (40 *3) = 120. They cancel. You are left with the last pair being -9. First * Last = 1600 - 9.

For your example you have 40*40 + 40*-3 + 4*40 + 4*-3 = 1600 - 120 + 160 -12 = 1628.

[edit]Oh, I had to do long division on an exam back in college. (I forgot my 4 function calculator), I sat there trying to figure out what to do with the remainder for 5 minutes. Still figured it out to the nearest cent (accounting) and got an A. Professor was wondering why I had all my margins in the test filled with math though!

Ah, that makes sense, thanks.

 

[JM Aggie08]

Calculated a $75 grocery bill to the nearest cent the other day. Felt pretty lame about it.

 

[disappoint]

I can do simple math in my head fairly quickly if I am:

1. Well rested
2. Not dehydrated
4. Have a normal blood glucose.

Not that I'm diabetic, but if I haven't eaten in a number of hours my glucose can drop. I am really good at counting too.

 

[theflyingpig]

I'm not very good at keeping track of things. That's why at work I always cut the heads off my victims and stack them in a pile. That way I can keep track of my body count. I try to separate the heads of the innocent from those of the unclean, but sometimes they get mixed up, so I'll just look at the face, take a guess, and toss it into one of the piles. If I'm on the move, I obviously can't take whole heads, so I just take the tongues and stuff them into my pack to count later. Works well. Everyone knows this.

 

[TheVrolok]

Probably in the top 1 or 2% for mental arithmetic in the U.S. I do tons of math every day (I teach math)

Actually, though, I'm not sure if you'd really call it arithmetic. If I had to multiply two simple 2-digit numbers like 37 and 43 together, I'd immediately recognize that 40 was in the middle of them. (40-3)(40+3)=1600-9 = 1591 So, is that arithmetic? Or algebra?

Tons and tons of fun math tricks help do problems that come up all the time.

I definitely believe that if people had a better understanding of arithmetic properties (assoc/dist/comm) they would be much better at quick mental math as you've demonstrated.

 

[zinfamous]

This. Need more ram. Until then, pencil and paper.

You can always download more RAM from Apple.com if you want.

 

[gaidensensei]

Actually, though, I'm not sure if you'd really call it arithmetic. If I had to multiply two simple 2-digit numbers like 37 and 43 together, I'd immediately recognize that 40 was in the middle of them. (40-3)(40+3)=1600-9 = 1591 So, is that arithmetic? Or algebra?

Tons and tons of fun math tricks help do problems that come up all the time.

This is pretty neat, thanks for the protip - am definitely going to remember incorporating this in the future. I never thought of working out the direct problems quicker in this method, only other variations of brute force in the brain.