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How do I subtract 12.12 from 20.00 in my...
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How do I subtract 12.12 from 20.00 in my head? I am making it harder than it is.
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>>7635730
Subtranct integers first, then substract one more, finally 100-decimals
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>>7635730
20 - 12 = 8
100 - 12 = 88
= 8.88

Eventually you learn how to handle it adaptively almost automatically. For example if it was 103.00 - 12.12, you could start with the decimal values first, or just recognize what they would do and just do 102 - 12, the decimal.
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>>7635730
>Hmmm subtract 12 from twenty, well there's 8.
>oh shoot, there's a decimal, k, let's just subtract that off the 8 too
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>>7635758
look at this retard
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>>7635758
>= 8.88
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>>7635758
then the decimal.**
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>>7635758
bait?

20-12 = 8
8-0.23 = 7.88
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>>7635764
>>7635765
>>7635771
Yep, I really blew it.
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>>7635758
>= 8.88
spotted the engineer
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>>7635781
consider_suicide.bmp
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>>7635758
I bet you are an engineer
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>>7635758
>=8.88
Moral of this story, mental maths in 2015 is retarded, stay safe and use a calculator.
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>>7635758
ouch
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>>7635758
L
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>>7635730
whenever i see a decimal i know to subtract one more off the integer.

if it's \$100 - \$25.36 i know automatically it will be \$74.xx then i just do the 100-36 in the same way knowing that it will be 70 < xx < 60 cents and get \$74.64.

it clicks really fast in my head. it's like the numbers narrow down into what they are, it's hard to explain
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>>7635758
>Eventually you learn how to handle it adaptively almost automatically

This is too good
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20 - 12=8
8 - 0.12 = 7.88
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>>7635758
kek
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The way I would do it mentally is:

20 - 12.12 = (20 - 13) + (13 - 12.12) = 7 + 0.88 = 7.88
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>>7636099
This. Makes it really easy for me anyway
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How do threads like this get serious responses, but threads about actual college level math subjects just get the op called a retard?
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>>7635781
should have played it off as if you where trolling m8
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>>7635758
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>>7635730

Go left to right

2-1 is 1
2.12 is bigger than 0.00 so borrow an extra 1 which makes 0
10-2 is 8
.12 is bigger than .00 so borrow an extra 1 which makes 7
10-1 is 9
.02 is bigger than .00 so borrow an extra 1 which makes 8
10-2 is 8
0 is 0 so the answer is now 07.88
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>>7636780
> Go left to right
nice try
back to >>>/pol/
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>>7635730
Take the 10's compliment of 12.12 = 87.88
20.00+87.88=07.88
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>>7635730
>american education
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>>7635730

Here's what I like to do in these situations (an informal treatment):

1. Just know what 100, (aka "a dollar"), minus the decimal part (treated as integer part here) is, cold. 1.00 minus "0.12" -> 100 - 12 = 88. -> "0.88". Whatever the difference ("change", in this case) ends up being, it will terminate with 0.88. Store that bit.

Now, this decimal bit (0.88) plus the above decimal bit (0.12) must of course be a dollar, itself. So whatever the integer part (the "dollar" part) happens to be, must add to this dollar, and also to the integer part of the smaller number (12.00) to wind up with 20. That should be easy enough once you get the above "storing" out of the way. 12 + 1 + x = 20, x = 7. Store this bit as well.

You could characterize the third operation as addition in this case, but I prefer to think of it as CONCATENATION: 7 AND-THEN 0.88, PUT-TOGETHER: Now all together

"\$12.12 is your total sir, out of \$20, hm my display isn't working but it doesn't matter because \$7.88 is your change. Here you go, have a nice day, sir."

-t. a cashier in a past life who would actually state these things out loud, which regularly impressed customers (sadly). It was also nice to be able to do because we did in fact have equipment fail once in a while. I also made use of elementary algebra a few times at a service desk when other people were getting stuck.
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>>7635730
>>7635758
You see, kids? This is why we need Common Core.
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>>7635758
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>>7635758

Oh my god this is fucking gold
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>>7635781
>>7635758

Sorry anon, couldn't resist.
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>>7635758
Maybe he's trolling
>>7635781
Holy fuck man
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Times them by 100 so you have whole numbers, subtract them as normal, then divide it by 100 to get what you need
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>>7637510
>times them

"Times" in the context of multiplication is a noun, not a verb. "[math]x[/math] times [math]y[/math]" means "[math]y[/math] added [math]x[/math] times". You don't "times" something, you multiply it. Let me guess, you're one of those faggots who refers to fighting someone in a video game as "versing" them because you think "versus" is a verb too, aren't you?
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>>7637533
what a nerd
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>>7637533
He didn't use it in the form of a noun, still a verb also versus is a preposition
A better example of mistaking a noun for a verb could be "I'll google that" prior to google being added in the dictionary as a verb (on top of having a definition that is a noun)
Maybe I'm wrong. Not that anon.
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Well my general rule of thumb is that the moment you see a decimal it has to be lesser than the number that you would get by subtracting without it.
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>>7637486
Kek
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>>7635730
>subtract 20
>???
>profit
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>>7635730
Count up, starting with decimals. So you get 0.78, leave 13, then you get 7 leave 20. So 7.78.
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>>7637533
THANK YOU!
I hear ignoramuses say this all the time at my school but I just bite my tongue so as not to alienate myself further.
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>>7637870
I already ran out of keks at the 8.88 guy, but here's a jej
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>>7637608
Not if negative numbers are involved.
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>>7635758
kill ur self it 7.88
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>>7635758
>>7635781
>>7637486
Say hi to Reddit!
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Like pic related but using only your brain.
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>>7635758
I saw this a few days ago and it's still funny
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>>7635730
that guy is jewmongous
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Pretend it is 2000- 1212. For some reason it works easier for me if you disregard the decimal points.
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>>7640086
its that fat guy who got kicked out of smashmouth and does those cooking shows where he gos from city to city to find food that makes him fatter

why is he mexican in your pic ?
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>>7635730
Just take the number below the one that adds to 10, since 1+9=10 you take 8, then 2+8=10 gives 7, 1+9 again and for the last number just take the one that adds to 10.
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>>7640168
When you get fat you get Mexican
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>>7638055
> THANK YOU
> IGNORAMUSES
Fuck off to reddit
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>>7635758
Topkek
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>>7635758
>mfw I mentally compute 7.88
>mfw see 8.88
>mfw give the benefit of doubt to sci
>mfw think im the retard.

oh wait
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>>7635758
This is why I love this board.
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>>7637533
>>7638055
or when people say 'minus' instead of 'subtract'.
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>>7635730
[math] 12.12+0.88=13 ~~ then ~~ 13+7=20 \therefore 20.00-12.12 = 7.88 [/math]
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>>7641400
>not understanding that it is not in fact ignorami as the plural of hippopotamus would have you believe because if its Latin root.
A quick Google search will verify this: "The plural is ignoramuses. Some dictionaries list ignorami as a variation of the plural, but this is a backformation by those who suppose since ignoramus comes from Latin that it would have the Latin –i plural. However, in the original Latin, ignoramus was a verb, not a noun, and would still have the -es plural."
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>>7635730
Imagine an abacus and move the beads around.
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>>7635839
>everyone is doing mental math
>i have to rely on calculator
>be 25 now
>finally mastering mental math in every day situations
>some mother fucker says something like this

i was way ahead of my time. Id even go as far as saying i was smarter than everyone else back then.
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>>7635758
Holy fuck.
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>>7642703
>>7641400
Former high school latinfag here to say stuff on this: ignoramus means 'we do not know' or 'we do not recognize'.
There is no such noun in latin according to what I looked up in my dictionary and the internet.
There are, however, two noun class called o-declension and consonantic declension (other names exist too). A word with o-declension ends in -us if not inflected (nominative singular) and for nominative plural, -us becomes -i. Consonantic declension ends with a consonant for nom. sing. and gets -es attached. So it's not entirely unresonable to think this might have been latin declension, apart from how there is little to find which suggests that this was used as a noun. Seeing how none of us care that there are 6 cases in latin, it's English salvaging foreign cultu- I mean languages.

Sage because irrelevant to natscience & math.