I know how I'd work this problem and I know the answer, but I'm not sure what methods are generally used in 5th gr and I don't want to confuse an issue. (btw, it's a bonus question and DS said they didn't go over how to do it.)

***About 7/10 of the US population (175,104,000) in 1991 believed saying A to be true. What was the total population?***

I'm so not good at 'teaching'. Even though I know how to do something, I'm not good at relaying the info in a way that makes sense. Guess I know where DS gets it .

Can anyone offer up 5th grade ideas for how this type of problem is taught?

One of the possible solutions using Singapore math would be

1) You say that 7 units = 175,104,000

2) From that you calculate how much 1 unit is

3) Then you calculate what 10 units are equal to

That's what I would do, but I have no idea how 5th grade math teachers might do it these days.

Does he know how to cross-multiply?

I'd teach him 7/10=175,104,000/X

Then you multiply the 10 times the 175,104,000=7 times x

1,751,040,000=7x

Divide both sides by 7

Thanks!! That's about where I was, but I wasn't sure if I was in the general grade area. Oh, and I love the 'teaching' instruction..."you say that 7 units...." LOL, I don't think I could mess this one up.

Have a great day!

Cross multiplication is the way my child was taught in 5th grade. Just like CAMom said.

Is cross-multiplication learned in 5th grade?? That was my very first thought, but I didn't think I could explain it even though I could do it. (I really have a hard time getting stuff out of my head and on to paper or in words.) I always remember "x over 100 is equal to is over of" from school, but that was many moons ago...

Thanks!

I wouldn't have thought cross-multiplication was learned in 5th grade these days, because of what DS7's teacher said to him about simplifying fractions being a 5th grade thing!

It is learned in 5th grade! Or at least my child learned it in 5th.

I have a distorted frame of reference because my 7th graders used to take full algebra and our 6th graders took pre-algebra. 8th graders all took geometry.

Well, apparently cross multiplication has not been taught yet. I now know this because when I asked DS if he knew what it was, I was met with a blank stare and "what's that?" LOL!

Of course, a lot of methods he's learning are new to me. The math curriculum is Everyday Math and there's something called the lattice method that I don't really get and DS doesn't really care for. <sigh> It doesn't take much to make me realize just how long ago it was that I was in school...

Thanks everyone.

No, it just doesn't take much to realize how screwed up Everyday Math is!

Lattice method just seems to assume that you're always going to carry a number chart or graph paper around with you, as far as I can tell. Aarrrgh!

You're not the only one who doesn't like the lattice method. This video helped me understand some of the weaknesses of EM and I'm making sure DD7 understands the traditional algorithms.

GAHHHH!

DS's 3rd grade teacher sent home some worksheets designed introduce kids to multiplication with the "partial products" method, and then later the "lattice method" ... before ever talking about the standard algorithm.

What a bloody nightmare that was. The teacher was very gracious, though, when I explained that we would be solving problems in the traditional manner, and that, if necessary, my son would take a zero on any tests where those methods would be required.

I couldn't believe it.

That video is superb -- thanks for sharing it here.

I'm a bit conflicted about all of this 'new' stuff. I suppose that it has it's place like anything else, but I think that parental involvement/support is less likely for ways that just don't make sense to them.

I love math and am not too shabby at it - I get it, much the same way my son does. I hate to pigeonhole him into doing math in a way that doesn't come naturally to him, because that's where the errors come in. Once he was shown the traditional algorithm (with proper explanation of what's what by DH, because I couldn't seem to explain it correctly), he got it. He still does math his own way in his head and for the most part is accurate, but he understands how to do it on paper now, too. His problem is in keeping everything lined up properly (turning the paper sideways is very helpful).

When he came home with the lattice method and partial products, there was so much writing on the paper that I couldn't make heads or tails of it....and DSs handwriting is an issue I'm pretty sure I've mentioned here before . DS will learn the other methods as they're taught because at least the students are being told to use whichever method works for and is easiest for them, which I totally support.

Glad to know I'm not really as old as I was beginning to feel...

JDax3 - in Rightstart Math (and in other maths and from other mathy-non US folk) I've read that DC should do math on grid paper. The math journal for RS math is 1cm grid squares. I photocopied it and made the boys a math journal for use w/ Life of Fred and Zaccaro books. You can buy 1cm square grid paper at Staples (bound).

Yes, I had heard a suggestion (maybe here?) about using grid paper to help with lining up of the problems. Now, if I could just get DS to use it. He's reluctant to try anything new, but needs time to warm to the idea - just a quirk he has. Just recently, I've noticed he's not totally opposed to turning a piece of notebook paper sideways, which helps immensely. Since I've already purchased a grid paper notebook, I'd like to see him try it and develop a habit of lining things up and then taper off of using it. All in good time.

Thanks for the tip!

Here's a link to a website where you can print your own graph paper in a variety of dimensions:
http://www.donnayoung.org/math/graph-paper.htm

In addition, the website has tons of different "styles" of lined paper, charting, etc. It's been a great resource for a couple of years. I'm just too cheap to buy a pad of paper that will only be used a handful of times.

Ohhh! This site is full of treasures. Great link. Thanks!