Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: I need help in the order of my teaching!!!
Replies: 19   Last Post: Sep 2, 1998 2:28 PM

 Messages: [ Previous | Next ]
 Gail R. Englert Posts: 28 Registered: 12/6/04
Re: ROUNDING NUMBERS
Posted: Aug 28, 1998 12:42 PM

Chris,
looking for a number that will be close to the "real" number, but easier to use
for quick mental math...

If you were working with 4 digit numbers, like 6781 or 4395, you would need to
find a multiple of 1000 that is close to the number you are working with. There
are 2 multiples "near" 6781 (6000 and 7000), and 2 "near" 4395 (4000 and
5000). Can you tell me the two multiples of 1000 "near" 2873?

To figure out which multiple is closer to the number you are working with, think
about a number line. If you made a number line for the numbers between 6000
and 7000, where would the middle of the line be? (It would be at 6500...) What
about a number line for 4000 to 5000? (That midpoint would be 4500.) What
would the midpoint be for the numberline between 2000 and 3000?

Now that you know what the line looks like, and where the middle of the line
is,you can figure out where your number is on that line, and then look to see
which multiple is closer to that point. For 6781, 6781 is past the midpoint of
6500 on the number line, and is closer to 7000 than to 6000, so we could say it
"rounds" to 7000. For 4395, 4395 is before the midpoint of 4500, and is closer
to 4000 than it is to 5000, so we could say it "rounds" to 4000. What do you
think would happen with 2873?

If you are working with even larger numbers, you can use the same number line
method, but you'll probably want to think it rather than trying to draw it...
For the number 456,789,123 is the number closer to 400,000,000 or 500,000,000?
The midpoint of that numberline would be 450,000,000 and your number is just a
little larger than that, so 456, 789,123 rounds off to 500,000,000.

Your problem used the number 123,202,624... what would the two multiples be?
Where is the midpoint? Which multiple is closer? Hope this helps you think
about what you are doing when you round. :-) Gail

chris BERNATHY wrote:

> PROMBLEM 123,202,624
> I've never done this before! I'm in the 5th grade. and my question is
> do I round this to the nearest million. would the answer be
> 200,000,000. or would it be 123,203,000. I'm confused and my teacher
> will not even show me an example. or explain any thing to me.
> can you help!
> Very much appericated, Chris

--
David and Gail Englert

@ @ genglert@norfolk.infi.net
! denglert@norfolk.infi.net
\<>/ genglert@pen.k12.va.us

"You've got to be careful if you don't know
where you're going 'cause you might not get there."
-- Yogi Berra