Need help with a Math problem!!

[HollyJoy]

Okay, I feel completely stupid!! Trying to help my 3rd grader with her homework and I am lost! LOL Anyone else have this problem?

Okay, so they are currently working on Using Mental Math: Using Tens to Add

The problems are as follows:

1. How does knowing 13=4+9 help you find 36 + 13 ?

and

2. How does knowing 38= 40-2 help you find 17+38 ?

I am completely missing something!!!

 

[twinklebug]

I'm lost too.
How are the questions phrased?

 

[mickeyboat]

1. 36 plus the four from the 13 = 40, then it is easy to add the 9 to get 49.

2. You add the 17 to the 40 to come up with 57, then subtract the 2 to come up with 55.

By breaking up the numbers to get to tens, it makes it easier to do the calculation, you don't have to worry about "carrying" number." But explaining it is tricky.

Denae

 

[RUDisney]

How about ... "they don't."

What silly questions!

When my kids get questions like this, I tell them to go ask their father. He usually makes something up that the kids are ok with writing.

 

[swanmom]

The idea is to make multiples of 5's or 10's which are easier to add.

For example, in the first case - you can rearrange the numbers -
Add the 4 (from the 13) to the 36 and then you have 40. Add the 9 (from the 13) to 40 and get 49.

In the second case, you add 40 (instead of 38)plus 17 which gets you 57 and then subtract the two and get 55.

For some people, it's easier to do 5's and 10's than to write colums and carry numbers. Hope this makes sense. It isn't easy to explain in writing.

 

[Breezy_Carol]

1. How does knowing 13=4+9 help you find 36 + 13 ?

and

2. How does knowing 38= 40-2 help you find 17+38 ?

It has been a long time since I did this but here is what I think they are getting at.....

For the first one, 36 + 13 = 36 + 4 + 9 = 40 + 9 = 49

36 + 4 should be easier to do in your head.

In the second I would break up the 17 also......

17 + 38 = 17 + 40 - 2 = 15 +40 = 55.

 

[jgmklmhem]

For #1 because 36 is a factor of 9 (4x9=36) it would show you that all you need to do is add another 9 to get 45 and then add that extra 4 from the first equation to get the answer of 49.

For #2 it is almost always easier to add a number like 40 than 38 so the first equation is showing you the easy relationship of instead of adding 38 just add 40 to the 17 and then subtrat the 2 off.

Explaining this in typing is hard but I hope you see my logic.

 

[Towncrier]

The problem (as I see it) with the math that they are teaching my kids is that they skip over the fundamentals and go right to the "tricks" that you can use to make math problems easier. I'm not saying that the tricks are wrong, but I still think that schools should focus on basic math skills (including memorization of multiplication tables). You can always learn the shortcuts later.

 

[Aneille]

The problem (as I see it) with the math that they are teaching my kids is that they skip over the fundamentals and go right to the "tricks" that you can use to make math problems easier. I'm not saying that the tricks are wrong, but I still think that schools should focus on basic math skills (including memorization of multiplication tables). You can always learn the shortcuts later.

The problem when I was taking math in elementary school and middle school was they didn't show us the tricks and because I wasn't adept at math I never picked up on them. I did everything out by hand. And I struggled with teachers going to fast on the blackboard. I do agree though that you should know your multiplication table.

I understand the question the OP is asking but I could never explain it. I figured out how to do this type of mental math on my own, unfortunately I was too old to actually use it to any advantage while I was school. I could never figure out how everyone else could do so much in their head!

BTW it wasn't like I was really really bad at math either, it was my tough subject. I took AP math from 6th-11th grade. When I finally figured this out, I couldn't believe I never knew to do it before! Too bad I was in college and didn't need to take any math courses.

 

[allie&mattsmom]

Yikes! LOL, that's even harder than the 3rd grade math word problem I was completely baffled over last week! I posted on here for help too!

 

[MinnieM3]

As a 3rd grade teacher, I think it "hurts" more students than it helps. My experience is that it confuses them more. My kids learn to add. I try to stick to the basics. I may mention various methods of solving problems, but don't "require" a specific method. I found those questions confusing myself. Sometimes the new "easier" is harder than the "old" way, to me!

 

[chrissyk]

The problem (as I see it) with the math that they are teaching my kids is that they skip over the fundamentals and go right to the "tricks" that you can use to make math problems easier. I'm not saying that the tricks are wrong, but I still think that schools should focus on basic math skills (including memorization of multiplication tables). You can always learn the shortcuts later.

In my old town, they referred to this "style" of math as "new math". My take on it is that everyone does this in their head as they get older. There is NO WAY that it should be taught as a method in school! How about learning to column-add and carry numbers? Is that just too old fashioned? Why not just hand them calculators and just forget about it if you're going to "teach" math methods like "new math" Sorry to vent, but this infuriates me!

 

[Aneille]

In my old town, they referred to this "style" of math as "new math". My take on it is that everyone does this in their head as they get older. There is NO WAY that it should be taught as a method in school! How about learning to column-add and carry numbers? Is that just too old fashioned? Why not just hand them calculators and just forget about it if you're going to "teach" math methods like "new math" Sorry to vent, but this infuriates me!

I'm not sure if 3rd grade is the place to teach these concepts because I also believe you do need to have the understanding of how to add by columns as well.

I am just not sure which way is easier to understand in the beginning. But I don't see anything wrong with teaching it at some point.

Not every method works for every child and I think its important to introduce various methods along the way as they progress in their understanding.

But there should be a standard for the basics. There is a large problem with children going to one school and learning "fundamental math" and then if they change school districts now they are being taught "new math". Sometimes in the same school district they will switch year to year as they try out "new math".

That is very confusing for a child. Sticking to a method is the most important.

But since most adults were taught "fundamentally" the concept of "new math" is going to be more difficult to do instictivly. But a child taught that way from the get-go may not have any trouble at all.

But again I don't know which way is the best way to learn from the beginning. I am sure there have been some limited studies somewhere but I haven't looked for them.

All I know is I am not really looking forward to elementary math when my child gets to it

 

[Sparx]

I'm so not good at math it isn't funny. Calculators were made for people like me! I am so bad at it, and that has given me a headache.

 

[HollyJoy]

Well, I think we figured it out.. For the poster who asked how the questions were phrased, I copied them word for word! Another poster said they are cutting straight to the tricks, which is so very true. My brain just doesn't think that way! Okay, so here are the answers that we came up with based on reading and re reading the chapter lesson:

1. How does knowing 13=4+9 help you find 36 + 13 ?

36 + (4+9)
(36 + 4) + 9
40 + 9 = 49

I used an example from the lesson, only using the numbers from the problem at hand. So by knowing that 4+9=13, you are able to break down 13 in the first step. TOTALLY CRAZY, I know. Much more steps to get the answer, I know. Even my daughter said it takes too long this way. lol


2. How does knowing 38= 40-2 help you find 17+38 ?

17 + 40 --round the 38 up to 40 by adding 2
17 + 40 = 57
57 - 2 = 55 -- you have to take away that extra 2

So by knowing that 40 - 2 =38, you are able to do this problem. MESSED UP!


Thanks for all the help!! I don't know if I will survive this year's math! lol

 

[Buckalew11]

I like the person who said, "It doesn't". LOL How true. All that would have done was confuse me. Just teach me how to add/subtract/multiply and divide.

I did learn a trick when learning to add my 9's which I still will do today but otherwise tricks like those mees me up. Rules are good though. I learned a rule here a few weeks ago as a matter of fact.

Anyway, I hope your child grasps this quickly and doesn't develop a math phobia like I did!!!!

 

[ElizaB39]

I LOVE new math. It is so much easier to explain to DS. It is abot rounding. Like when he is memorizing sums, 8+7 always seems to be hard so I say what is 7+7 and then add 1 to that. That to me is mental...

I menat to say mental math!