Do My Homework, Please

olds

Elite Member
Mar 3, 2000
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OK, I am in second grade and I got this as an assignment. I get where the bottom number comes from (one with arrow) but where does the number above it come from?

R9wkKZP.jpg
 

allisolm

Elite Member
Administrator
Jan 2, 2001
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10-7=3 10+1=11 3+1 =4
10-7=3 10+6=16 3+6 =9
10-6=4 10+5 =15 5+4=9

and so on
 

MagnusTheBrewer

IN MEMORIAM
Jun 19, 2004
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Please explain how it's easier to subtract from ten than any other number. The answer is we don't subtract because it's easier to ask yourself what can we add to the smaller number to make it equal the larger. One step, no subtract from ten hocus pocus and then add the amount in the ones place. Like I said, the original method is new math fail.
 
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Red Squirrel

No Lifer
May 24, 2003
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www.anyf.ca
I suck at doing math in my head, even basic math, and these weird ways don't make it any easier. I usually hate playing math oriented card games for that reason since it makes me feel like an idiot, it's even worse trying to do it in your head when under pressure. While it's obviously good to understand how to do this manually I think the easiest is the traditional way of stacking the numbers then you do one column at a time. Carry over the 1 etc. That style.

But in the real world you would feed that data in a computer. Whether it's a calculator, or a computer program, etc.
 

MagnusTheBrewer

IN MEMORIAM
Jun 19, 2004
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I suck at doing math in my head, even basic math, and these weird ways don't make it any easier. I usually hate playing math oriented card games for that reason since it makes me feel like an idiot, it's even worse trying to do it in your head when under pressure. While it's obviously good to understand how to do this manually I think the easiest is the traditional way of stacking the numbers then you do one column at a time. Carry over the 1 etc. That style.

But in the real world you would feed that data in a computer. Whether it's a calculator, or a computer program, etc.
Except in my version of the real world, I work with my hands in a messy environment and being able to do simple math, conversions and, fractions in my head is a critical necessity.
 

sandorski

No Lifer
Oct 10, 1999
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It is what is left over after subracting the > 10 amount from the final outcome.
 

SKORPI0

Lifer
Jan 18, 2000
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subtraction.svg


Subtract subtrahend from 10. ;)

example from OP picture.

11-7= 4; 10-7 = 3
15-7=9; 10-7 = 3
15-6=9; 10-6 = 4

As already explained by MagnusTheBrewer..
 

MagnusTheBrewer

IN MEMORIAM
Jun 19, 2004
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subtraction.svg


Subtract subtrahend from 10. ;)

example from OP picture.

11-7= 4; 10-7 = 3
15-7=9; 10-7 = 3
15-6=9; 10-6 = 4
That brings up another pet peeve of mine, "manglish." The term I made up to define words like minuend and, subtrahend. I understand mathematical relationships very well but, start talking about those relationships using manglish and my eyes glaze over and, I start thinking homicidal thoughts.
 
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Carson Dyle

Diamond Member
Jul 2, 2012
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Both number are just the difference (distance) from 10. Add them to get the answer. Pretty sure this is exactly how I do subtraction in my head.

137-88 = 37+12 = 49

Doesn't have to be 10 or 100. Any number in between will do. Say you're subtracting dates:

1915-1753 = 115+47 = 162
 

Humpy

Diamond Member
Mar 3, 2011
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You are adding two numbers, in the op, the number is subtracted from ten and the added the the number in the ones position. A small difference of perspective.

I think he just didn't show the step of pulling the 37 down, then subtracting the 88 from the remaining 100, before adding 37 and 12.

I just know the answers in the OP. Once it gets to something like 137-88 I look at the values on either side of 100 and add those. The number line is easier for me to visualize, the OP is teaching the same thing in a slightly different way.

Interesting.
 

zinfamous

No Lifer
Jul 12, 2006
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I'm all for different perspectives when learning math but, this method adds an extra step and another chance to make a mistake. It's new math fail.

small numbers like that, it's better to just memorize those differences, but when you get to larger numbers, it is much easier and much faster to convert to 10s and keep track of the difference.

It just is.
 

mxnerd

Diamond Member
Jul 6, 2007
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What's the purpose of this kind of math teaching? It does not inspire anything.
 

MagnusTheBrewer

IN MEMORIAM
Jun 19, 2004
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What's the purpose of this kind of math teaching? It does not inspire anything.
The general approach is to present mathematical concepts using different perspectives because not everyone learns the same way. Teachers spend a great deal of time learning different techniques such as this to better teach and communicate with their students. Overall, it's a good thing.
In the dark ages when I grew up, there was one and only one method for learning math. I was in hs struggling with trig before I learned there were alternative ways to approach the information. A little yellow carpenters handbook got me an "A." Once again, the block had been "manglish."
 

UglyCasanova

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Mar 25, 2001
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What's the purpose of this kind of math teaching? It does not inspire anything.


I’m not sure why we’d be worried about inspiration, but I think the goal like Magnus said is to offer different approaches where it may click with somebody more. The push is to get the kids to actually understand the math that they are doing vs just going through the motions. Even if they get right answers a lot of times kids can lose track of why it’s a right answer and what it is they just did.
 

VirtualLarry

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Aug 25, 2001
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When I was in class, we MEMORIZED things like multiplication between the numbers 1 and 12 (and every combination in-between). We were speed-tested, too.
 
Feb 25, 2011
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When I was in class, we MEMORIZED things like multiplication between the numbers 1 and 12 (and every combination in-between). We were speed-tested, too.
Great.... what's 13 * 13 and how do you know that's right? No calculator.

That's the point of all this - teaching kids why, not just what.