Math 2.0 Subtraction-Decomposing -- HELP

[Anonymous]

My kid brought home this today.

70 ^ ^ < < < (those are actually up arrows and left arrow).

What?

Answer is 47 of course!!!

[Anonymous]

Anonymous wrote:My kid brought home this today.

70 ^ ^ < < < (those are actually up arrows and left arrow).

What?

Answer is 47 of course!!!

This makes sense if you have a 100 number chart and go up two rows by 10 to 50 and over three to the left so 70 -23 =47. This makes more sense then OP's question that the PP teacher also couldn't figure out.

[Anonymous]

I hope OP posts the answer.

[Anonymous]

Anonymous wrote:Hi, I need to help my son and I do not understand decomposing. I know decomposition, but not this decomposing. Someone please help me! For example - the worksheet my son brought home:

For the problem:
698
-327

The sheet asks him to fill in the blanks:

_ _ _
-_ _ _
[u]
_ _+_ = _

I understand decomposition: 600 + 90 + 8 minus 300 + 20 + 7. I do NOT understand the problem the way the worksheet laid it out. with the two hundreds numbers going to a ten plus a one to equal a one digit?

OP here. I heard back from her teacher. Each line is supposed to have the entire expanded number (600 in the first line, 90 in the second, etc.) I am used to putting one digit on each line which is why this was confusing. She had other math sheets which only had one digit per line so it was inconsistent. Anyway, it is expanded notation and then subtraction. Gota love the new terminology.

[Anonymous]

Anybody else think of rot whenever they hear the new math lingo? Such an unfortunate term.

[Anonymous]

Parent of a younger child here - OP, can you walk me through how your son is supposed to do that subtraction problem - I do not recall those terms from my days!

[Anonymous]

OP here for the above PP:

698
-327

The sheet asks her to fill in the blanks:
600 + 90 + 8
-300 + 20 + 7
____________
300+70+1 = 371

or if you need to borrow:

672 minus 394

600+70+2 500+160+12
-300+90+4 -300+ 90+ 4
_________ __________

200 +70+8 = 278

The crazy thing is, my daughter learned math the traditional way and it is just this year in 3rd grade that they are changing things up. She can do math the old way and we are all learning this new way together.

[Anonymous]

I still don't get the point of this new way.

[Anonymous]

Wow -- I don't understand the "need to borrow" way. But I like that we are having children look at numbers in a different way than we did under the old method. I'm assuming it will help with higher level math, which I don't get.

[Anonymous]

OP Here - the "need to borrow way" is a little messed up as the numbers ran more together when I submitted than when I was typing them down. The expression on the right side of the original problem is the revised expanded notation once I borrowed "10s" and "100s" so the 600 became 500, 70 became 160 and 2 became 12.

[Anonymous]

this is ridiculous. Can we just subtract the normal way?!?!?

I have 2 engineering degrees, work as an engineer, got great scores on the math SAT, got 5 on the AP calculus test and the normal way with borrowing, etc. has served me well.

LOL. Yes, my left brain kids look at this stuff with a "why are we doing this?" annoyance. They can do normal math very fast and often in their heads. I've had to tell them to look at it as a puzzle or a riddle which seems to have worked. Your goal is to figure out what the teacher wants you to do and how someone else might think about math.