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Teaching percents
Old 03-29-2011, 10:45 PM
 
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How do you teach percents? Some of my kids understood, and others didn't. I'm wondering if there are some other methods out there? How do you do it?

What is 20% of 30?
What percent if 15 of 54?
Eight is 23% of what number?

Thanks!
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Old 03-31-2011, 01:59 AM
 
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I think they have to have a good handle on division and fractions, knowing that 10% of a number means that number divided/split into 10 equal parts and that it's the same as taking 1/10 of it!

That being said, I usually teach them benchmark percents...for example, to do 20% of 30, you do 10% which is 3 and then multiply that by 2 to get 20%! As long as they know the easy ones: 10%, 50%, etc...the others are easier to computer. I don't think 5th graders really need to be able to do the last example you gave...maybe that can be an extension for the higher kids.

Honestly, if my kids could just be able to write a number as a frac, dec and percent, I would be thrilled
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percents
Old 03-31-2011, 07:56 AM
 
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Thanks for the reply! I taught benchmark fractions but didn't think to teach benchmark decimals, so I will go back and do that.
Quote:
Eight is 23% of what number?
These are problems in our book...


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make it fun
Old 03-31-2011, 07:40 PM
 
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after introducing a chart that shows how percents, decimals, fractions, ratios are related, we "go shopping and then go to dinner"

use the weekly circular from the local grocery store (i grab 30 from the front door area), create a shopping list...the kids add (decimal review integration), and then I have them blindly pick a 'coupon' from a deck of index cards I make. These have % off amounts. They find the discount and then their new total.

Then we 'buy' clothes from Justus or American Eagle and find a discount coupon- a la Kohls-to deduct..


after all this shopping, we have to eat...bring in local menus, order food, then do two addition operations with percents.. 1-add the sales tax to the dinner. 2. calculate an 18-20% tip to add to the check.
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Old 03-31-2011, 08:32 PM
 
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For the grade you teach, do you write equations with a letter variable? We don't teach this until Jr. High...

Quote:
What is 20% of 30?
N = 0.20 x 30
N = 6

Quote:
What percent is 15 of 54?
N = 15 54
N = 0.28
= 28%


Quote:
Eight is 23% of what number?
8 = 0.23 x N
8 0.23 = N
34.78 = N


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Old 03-31-2011, 08:53 PM
 
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I teach my 5th grade students the same way that Suezie does.

I also make sure that my kids understand that "per cent" means "part of one hundred". Whenever we say 20%, we also say that is 20 parts of 100, or 20/100. We can rewrite this as 0.20 (twenty hundredths). it helps them when we are going between percents, decimals and fractions. It keeps in mind for them that percents are just another way to write a hundredth decimal and fraction. I have found that it also makes it easier when we are going to find percents of numbers and fractions as well.
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percents
Old 04-12-2011, 08:54 AM
 
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Thanks for the help! I went back and added in some of your suggestions. I think it's just a matter of practice...which we don't have time for with the racing, I mean, pacing guide.
As I read through your answers, it seems I'm the only one having them set it up as an equation (What is 40% of 70):

40% = x
100.... 70

then they multiply diagonally and divide by the left over number...

(I had to put the zeros so that the 70 would line up properly)

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How about...
Old 04-12-2011, 09:08 AM
 
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40% is equal to 40/100 then multiply by 70?

40/100 x 70/1

Show them how to "cross out" zeros and the rest will be easy. Well, I THINK it will be easy.

40/100 x 70/1 ("buddy up" zeros on 70 and 100 to cross out)

40/10 x 7/1 (multiply across)

280/10 (divide or cross out zeros again)

28

Hope this helps.
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