Need ideas on teaching percents

[seema]

I have tried so hard to explain percents to my dd 13, she gets the main concept, but when applying it to word problems she is struggling. So in problems figuring out if the part or whole is missing is really hard for her, once she understands that she can then solve it.

I am not sure how to make this any easier for her? appreciate any ideas.

[kbutton]

Can you make a part to whole type of diagram/model that she fills in each time she looks at a problem so that she can actually see the missing piece? Or, is the problem telling which is part and which is whole? (A diagram might still help with that.) 

 

There may be a diagram in here that makes sense: https://www.google.com/search?q=part+to+whole+diagram+for+percent+problems&rlz=1C1KYPB_enUS597US601&espv=2&biw=1440&bih=731&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwib3ayTyNzJAhUHVh4KHeTFDiMQsAQIGw

 

 

[hornblower]

can you post a sample question that she's had trouble getting started with? 

[seema]

Can you make a part to whole type of diagram/model that she fills in each time she looks at a problem so that she can actually see the missing piece? Or, is the problem telling which is part and which is whole? (A diagram might still help with that.) 

 

There may be a diagram in here that makes sense: https://www.google.com/search?q=part+to+whole+diagram+for+percent+problems&rlz=1C1KYPB_enUS597US601&espv=2&biw=1440&bih=731&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwib3ayTyNzJAhUHVh4KHeTFDiMQsAQIGw

the problem is she gets confused figuring out which is whole and which is part.

will try diagrams, thank you.

[seema]

can you post a sample question that she's had trouble getting started with? 

 

 

10 is 5% of what number?

40% of what number is 82?

[hornblower]

definitely diagrams. My kids always do their math on graph paper so when starting out percentages, we'd draw a rectangle 10 boxes long & 1 box high and then mark what we know along the rectangle... So we'd mark half of a box & say this is 5% and the problem says its value is 10...  So how much is the whole thing going to be?  


they also did Chalkdust and the instructor explains a bunch of times that when you see the word "of" in math, that means multiply. So if they were setting up the equation for the first they'd say  10 is/equals 5% times X  

And they also knew that to do anything with percents you convert to a decimal. 

So a combination of diagrams & maybe just rote rules (perhaps on an index card for her to refer to? "of" means "times"; convert % to decimals... ) will get her going & then practice lots.. 

 

[Mom28GreatKids]

I always teach them thw ratio way- % over 100 = is over of. So 10/x = 5/100, cross multiply and then solve for x. This is howbI learned and it has always stuck with me.

[Mom28GreatKids]

I always teach them the ratio way- % over 100 = is over of. So 10/x = 5/100, cross multiply and then solve for x. This is howbI learned and it has always stuck with me.

[Vida Winter]

10 is 5% of what number?

40% of what number is 82?

 

Get her used to translating "of" to "x" (where x means the multiply symbol).

Also translate "is" to "="

Also translate "what number" to "n" or a similar variable

 

So in this case,

 

10= (.05)(n) then divide each side by .05 to get n

 

on the next one:(.40)(n) = 82  then divide each side by .40 to get n

 

Practice converting between decimal and % (and back the other way). If a number is expressed in %, take the % sign off and move the decimal two places to the left.

 

Ex:

67% =0.67

3% =0.03

0.3% = 0.003

 

Also show that percent means "per cent" or "per 100", or "a number divided by 100" 

Ex:

67% = 67/100 = 0.67

7% = 7/100 = 0.07

 

You can also talk about percentages needing to add up to 100%

If you have used 85% of a 20 pound bag of flour, what % is left?  100% - 85% = 15 %;   (.15)(20 lb) = the remaining flour

 

With practice, a lightbulb will switch on at some point.

[Guest]

If 82 is 40%

Then X is 100%

__________________

 

X= 82×100/40 (This is how I learned)

 

Saxon uses diagrams. I have shown my son both ways. The diagrams make it more visual and provide more conceptual understanding. The above method is more mechanical but faster.

 

Note: The numbers are supposed to line up according to place value but it messes up when I hit post.

Edited December 15, 2015 by Guest

[Carol in Cal.]

First of all, sometimes it is really helpful to have an example in mind.  For instance, 50% is the same as 1/2 which is the same as one divided by two which is the same as 0.5.  She can use that as a model to test anything she does.

 

"of" always means 'times'.  That's the main thing to remember.  'Is' means 'equals'.

 

Then if she can just write the sentence as an equation, she will be all set.

 

Like this:

 

10 is 5% of what number?

10 = 0.05 x A

So 10/0.05 + A

 

40% of what number is 82?

0.40 x A = 82

So A = 82 / 0.40

[ElizabethB]

I like to bring money into it!

 

12 cents of one dollar is 12 percent. 12 / 100. 1/4, 25 percent, 25/100. A lot of examples foing back and forth and problems with tangible money things before doing weird random problems that make no sense to a young mind. If they have a favorite thing they like to purchase, I like to bring that into it, too.

[Guest]

First of all, sometimes it is really helpful to have an example in mind. For instance, 50% is the same as 1/2 which is the same as one divided by two which is the same as 0.5. She can use that as a model to test anything she does.

Saxon helps them make these connections also. I like that too!

[merry gardens]

Shopping sales provides real-world application. You could do this in stores or over the internet.

 

"If the item cost $10 originally and is on sale for 30% off, what will it cost, before sales tax?"

 

If sales tax is 7.5% and you buy $100 worth of taxable items, what will the total cost be?"

 

At 13, I'd allow a calculator or calculator app, which makes it far easier to calculate the prices while shopping.