Monday, December 04, 2006

Subtract This, Pal!

Solve this problem in two different ways, and write about how you solved it:


That was the problem that nearly drove my son to tears tonight, and made me want to go out and find Misters Houghton and Mifflin, and subtract some consciousness from their respective noggins.

He wasn't upset because he couldn't solve it. He did it in his head. Then he did the two-line subtraction that he's known how to do since he was six.

He was upset because he now had to figure out another way of solving it. Another way? What other way is there? It's subtraction, for fuck's sake. You remove one amount from another amount. End of story.

What do I tell him now? 'Let's figure out some bullshit way of making this subtraction problem far harder than it needs to be, because apparently we have to know more than one way to do this. Is there a politically correct way of subtracting? Maybe we should add, and keep adding until we get beyond infinity, and maybe eventually the number will come all the way back around and end up a factor of eighteen away from the original number!'

Screw it. Do the math. I'll check it. You'll get it right anyhow. Every time I think I find a mistake, you show me that I'm wrong about it.

Sometimes I wish they would leave my child behind.

Maybe then he'd be free to pick up a book and start learning.



Anonymous Anonymous said...

how do you subtract in a different way?

i'm already feeling stupid and i have calculus...

please report back on examples of the solution(s). i'm thinking i'm going to cry.

12:57 AM  
Blogger B-logger said...

The only thing I thought of when I read that was 2 possible ways you can solve it in your head... first, subtracting down...

307 - 20 = 287.
and ...
287 + 2 = 289.
Therefore the difference is 18.

Adding up....
Another way to solve it in your head is to say:
289 + 20 = 309.
ie the difference is 18.

I have no idea what grade at school this is so I could be way off.

Of course one way could be with a calculator, the other with paper ;-)

1:08 AM  
Blogger Balloon Pirate said...

I think b-logger has something here.

I come from a famil of engineers, where math problems are solved sequentially: subtract the ones column, then the tens, then the hundreds, et c.

Thanks b-log!

cad: I feel stupid AND contagious.


6:48 AM  
Blogger Madame X said...

This comment has been removed by a blog administrator.

7:54 AM  
Blogger Madame X said...

OK so the delete was me because I was going to agree with B-logger but then I realized that I misunderstood...Nevermind

OK so

307 - 289 = 18
18 + 289 = 307

That's what I was going to say!

7:59 AM  
Anonymous Anonymous said...

strange... the whole point of math is simplification. The only way to do that problem different is to complex it, and guess what? It is still the same !@#$ problem. What the !@#$ were they thinking

!@#$ is in deference to my good manners rather than saying what I really think *L*

8:06 AM  
Blogger Madame X said...

I forgot to say that the instructions were to solve the PROBLEM 2 ways not to subtract 2 ways.

8:08 AM  
Blogger Leesa said...

Here is how I see it:



Add 7 + 11 = 18

You intuitively know that 307 is 7 more than 300 and that 289 is 11 short of 300, so it is easier to solve in your mind. I think that may be one way to do it.

b-logger had an interesting way as well.

9:33 AM  
Blogger Heidi the Hick said...

Ok I see numbers and all I can think of is:

blobbity blah blah blabby blah blah blobbity fuck.

Seriously. I can't tell you how many times this scene has played out in our house. Last year the response was, "Tell you teacher that this is bull. No wait, let me write the note in your workbook. No it's okay, you won't get in heck sweetie, tell your teacher to call me."

This year we both look at each other and agree that the best way to solve this problem is to get out the calculator, write down the answer, and inform the teacher that it's HIS JOB to teach my kids how to do math, not to push these bullshit text books that only confuse the matter.

Gah. Heart palpitations. Must go now. grrrrr....

9:47 AM  
Blogger United We Lay said...

I don't know how to do it more than one way, either. Seriously, this is driving me nuts. How else would the teacher want him to do it? The traditional way works just fine, and a second way might just confuse him, which obviously it did. This NCLB stuff is crap. If a kid knows how to do it one way, fine. Let him use the way that works best for him, especially since that's what he's going to do in a real-world situation anyway. I highly doubt that someone's going to put a gun to his head and tell him he'll shoot if he doesn't know 2 ways to solve the problem. Schools are doing a lot with critical thinking and problem solving, but I think at times they go a little overboard. I have more to say, but Senor Stinky is waking up from his nap.

11:59 AM  
Blogger United We Lay said...

Madam X,
That would be my thought but maybe I'm reading too much into semantics. The way you did it, you made a different problem, which is not what the teacher told him to do. The teacher said, solve THIS problem:

307 - 289 =
If you change it to 18 + 289, then aren't you changing the problem? Maybe I'm reading too much into this.

12:02 PM  
Blogger AlwaysArousedGirl said...

We're only on addition yet, but here's what they want my kid to do:

47 + 39 =


40 + 30 = 70 and 7 + 9 = 16,


70 + 16 = 86

There is no carrying. We don't even MENTION carrying. We don't even THINK about carrying.

Evidently this emphasizes that we are not adding (using the problem above for an example) 4 + 7, but instead we are adding tens, ie, 40 + 70.

Does this make sense?

Can it be translated to subtraction?

1:40 PM  
Anonymous Anonymous said...

Funny you should mention this, me and some pals were discussing that subtracting is always harder than addition and that's because subtraction is un natural and that it is a manmade conceit because man cannot tolerate zero as it is too final so invented the idea of infinity in both directions to ease the sense of ennui.

Subtraction should be banned.

5:26 PM  
Anonymous Anonymous said...

stop! everyone stop it with the math!!!

i have a headache.

here we are now, entertain us...

6:57 PM  
Blogger Heidi the Hick said...

a mosquito my libido a denial....

7:33 PM  
Blogger B-logger said...

This comment has been removed by a blog administrator.

9:47 PM  
Blogger Jessica said...

My hunch is that Leesa is closest. Most state standards include objectives about rounding as well as precision in basic math. Any chance that your son has talked about rounding in class lately? That would help.

Personally, I think you should tell a story about it. E.g. I took 307 dollar bills to New York and threw most of it up in the air. Two hundred eighty-nine people mobbed me, and all I had left for the cab ride home was 18 lousy bucks. (Assuming of course, that the mob was nice and civilized and each person -- named Anna, Bob, Cody, etc. no doubt -- only took one dollar apiece.)

11:38 PM  
Blogger terry said...

anonymous?? that was me!

suddenly, my identity has been erased from all the comments i posted tonight.

i blame the math...

12:07 AM  
Blogger terry said...

i was the anonymous with the headache, btw. i notice that many people are suddenly anonymous tonight..

12:07 AM  
Blogger GC (God's Child) said...

just wanted to say I endorse Heidi's solution. This math problem looks like a trap to me.

3:05 PM  
Anonymous Anonymous said...


there's an interpretive moment for you

when i read the question i read solve "307-289"

that is a single equation

i didn't see the instruction:

break this equation down

307-289 is not the same equation as (300+7)-(200+89)

it is not the same equation as 307=289+n

it's a stupid and imprecise instruction. math requires precision. unless you are given specific instruction to be imprecise.

i teach my kids to do stuff like

300-289 then add 7 in order to do math in their heads all the time - but that is not what the instruction you cited said

3:50 PM  

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