Need Help ! 2nd grade math, for chrissakes.

[3Hotdogs]

How does one use Associative and Commutative Properties to solve a multiplication problem?

[LuckyCharms]

1. .

https://sciencing.com/associative-commutative-property-of-addition-multiplication-with-examples-13712459.html

[MissB]

2. Associative would be grouping

And commutative would be putting the numbers in different order (because it won’t affect the result).

Can you provide an example problem you’re trying to solve?

[3Hotdogs]

4. Mark wrote the hightest score he made on his new video game as the product of 70 x 6,000.

Use the Associative and Commutative Properties to show how Mark can calculate this product mentally.

[jcgoldie]

7. it means... you can break it down to powers of 10

70 * 6,000 = 7 * 6 * 10 * 1000 = 420,000

[DeminPennswoods]

10. Or

7*6,000*10=420,000

[jcgoldie]

13. right

whatever way is easy for you.

I used to deal craps... you have to do everything mentally and pay people fast... those dealers all know these properties without having a clue what they are actually called.. paying peoples prop bets is just a lot of breaking shit down to the times tables you know.

[DeminPennswoods]

15. I knew these properties when I was

in grade school, but never made use of them until my dad showed me how easy it was to do. He probably didn't know what the arithmatic properties were called either. Now I use that all the time when grocery shopping to estimate what I'm spending or to do other quick calculations. Occassionally makes me feel superior, too.

[hlthe2b]

22. Yeah. I learned to grind through it and I was fast at doing so. But, I do see how this method is

helpful. OTH, with such a calculation, I was probably doing this method and hadn't really thought about it (calculating the 'front' of the equation and then sorting out the zeroes, so-to-speak)

[struggle4progress]

9. .

It's 420000:

70 x 6000 = (7 x 10) x (6 x 1000) = 7 x (10 x (6 x 1000))
= 7 x ((10 x 6) x 1000) = 7 x ((6 x 10) x 1000) = (7 x 6)x (10 x 1000)
= 42 x 10000

[CincyDem]

19. 7x6 then add 4 zeros. n/t

[3Hotdogs]

3. When I was in 2nd grade, I was trying to hide, taking off my shoes to count to 16.

[jcgoldie]

5. ...

the associative property of multiplication means you can multiply factors in either order and the result is the same (ie 3 * 4 = 12 ... 4 * 3 = 12)
Commutative means if you have more factors you can group them any way in multiplication... (ie 2 * 3 *4... (2*3)=6*4=24 ... 2*(3*4) = 2* 12 = 24... (2*4)* 3 = 8 * 3= 24

These properties are also true of addition but not of division or subtraction.

[FakeNoose]

6. It means you multiply and divide first, before you add or subtract

First do any function that is inside the parentheses.
Second do any multiply or divide function.
Third do any add or subtract function.

But the parentheses supersedes everything.
(Any addition or subtraction that are inside the parentheses - those get done first.)

Good luck!

[LuckyCharms]

12. Please excuse My Dear Aunt Sally...P M D A S

[FakeNoose]

25. Yes that's it

However the hard part is remembering what the letters stand for in the acronym.

[3Hotdogs]

8. Thanks, guys.

[Luciferous]

11. As someone who has had to help their child extensively with math, I recommend

Kahn Academy's website. It's free and there are videos that clearly explain concepts

https://www.khanacademy.org/math/early-math

[BlueSpot]

14. Wow. I remember people complaining about "new math" but I don't know that I ever saw an example

I think I just did. Jeepers, they just taught us how to multiply the numbers. With all those zeroes, it's super easy.

To people with experience on both sides, is this way really better? How does it go when the numbers don't all end in zeroes? Seems like extra steps must be involved - like getting to the zeroes first and then having to go back and pick up the odd seventeens or whatever.

[OhioBlue]

20. I don't think it is really a matter of which way is better.

Honestly, the way that we were taught to figure math problems is still taught, it is just expanded upon and different methods are taught. I think it helps with critical thinking and logic. I will tell you... I volunteered in Santa Secret shop for a few years and by the time these kids were in 4th/5th grade, they could add their purchases in their head quicker than any volunteer could add on their cell phones or on paper. lol.

[hlthe2b]

23. That is interesting because over the past couple of decades, I've yet to encounter a sales clerk who

could even attempt to do so when electrical outage had the computerized registers out of commission. I would do so verbally with them and add the total for a dozen or so items, to which they'd agree (though I'm not sure they were actually trying to verify). Then when I did the sales tax percentage, either in my head or on paper, their eyes just glazed over.


I hope that is no longer the case. But, then I am a health care professional and I'd no more trust most ER and ICU staff to head or hand calculate drug doses for a continuous IV drip when the computers go haywire-- without double checking-- than I'd trust the average person on the street to safeguard my life savings.

[DeminPennswoods]

24. The properties are old math

I remember learning them in school in the '60s.

[foo_fighter999]

16. Depending on how the instructor wants the answer.

they may want it broken down and labeled as:
70 * 6000 =
Associative: (7 * 10) * (6 * 1000) =
Commutative: (7 * 6) * (10 * 10000) = 420,000 = waaaayyyy less money than Trump owes

But since it's only second grade, you might want to leave that last bit off. If it was third grade, I'd say leave it.

[crickets]

17. Hee.

Welcome to DU, foo_fighter999! Great name.

[foo_fighter999]

18. Thanks!

Love the Foo Fighters. And these days, there's a lot of Foo to Fight, lol. (Not here, obviously. Out in the real world. Sigh. So much stupidity, so little time.)

[Mossfern]

21. I'm glad that I'm old enough

not to bother to learn this.

And to think - I was teaching math to adults to pass the GRE's before I retired.
At that point, the test used the "old fashioned" method of arithmetic.

I was amazed at my students from South America who did long division upside down.
It worked for them.

[lillypaddle]

26. YIKES

I have a college degree, I don't need no stinkin' 2nd grade math.

Funny thing is that my 8 yo granddaughter is in a gifted and talented class for math. Did we actually do this stuff back in the old days? I must have blocked it all out.