Do My Homework, Please

[olds]

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?

 

[allisolm]

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]

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.

 

[UglyCasanova]

Honestly it’s what we do in our heads anyways. Break it up into 10’s.

 

[MagnusTheBrewer]

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.

 

[Red Squirrel]

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.

 

[shortylickens]

I learned by adding negative numbers.

I'm kinda weird.

 

[MagnusTheBrewer]

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]

It is what is left over after subracting the > 10 amount from the final outcome.

 

[SKORPI0]

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..

 

[UglyCasanova]

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.

To me that is the easiest way to work it out on paper. In my head though I think the way in the OP is easier.

 

[MagnusTheBrewer]

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.

 

[Carson Dyle]

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

 

[MagnusTheBrewer]

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

you're using the number line approach which works just fine but, is not the method shown in the op.

 

[Carson Dyle]

you're using the number line approach which works just fine but, is not the method shown in the op.

Yes, it is. It's exactly what is being taught in the OP.

 

[MagnusTheBrewer]

Yes, it is. It's exactly what is being taught in the OP.

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.

 

[Humpy]

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]

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.

 

[olds]

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..

Ah, thanks.

 

[mxnerd]

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

 

[MagnusTheBrewer]

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]

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]

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.

 

[dave_the_nerd]

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.