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 Post subject: PercentagesPosted: Fri Oct 23, 2009 1:33 pm

Joined: Thu Jan 22, 2009 7:57 pm
Posts: 156
We have come across a few of these questions: Eg. a grid of 32 squares has 20 shaded. What is the percentage of shaded squares?
The answers are all very close, so guestimating isn't an option. Is the only way to do the long division of 20/32?
That would take me a few minutes to complete with a pencil, never mind my DS in an exam!

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 Post subject: Posted: Fri Oct 23, 2009 2:01 pm

Joined: Fri Jan 25, 2008 8:36 pm
Posts: 247
Location: moseley
Hi

I'm no expert but i would do this by :

20/32 simplify to 5/8
1/8 as a % is 12.5
5/8 = 12.5 x 5 = 62.5%

I'm sure there may be a better way to do this and someone more able will come and help.

Fm, yoyo......where are you?

mm2

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 Post subject: Posted: Fri Oct 23, 2009 2:19 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8113
Hi mm2

seems a sensible way to do it!!!

It is worth kids knowing what the equivalent percentage of common fractions (other than 1/2 and 1/4!) is:
eg 1/8 =12.5%
1/6 = 16.6%
1/3 = 33.3%
1/12 = 8.3%

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 Post subject: Posted: Fri Oct 23, 2009 2:43 pm

Joined: Thu Jan 22, 2009 7:57 pm
Posts: 156
Thanks for that. He hasn't done much percentage work at school so it's all down to me. That tip should be very helpful.
Thanks

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 Post subject: Posted: Fri Oct 23, 2009 2:49 pm

Joined: Wed Feb 27, 2008 8:59 am
Posts: 2001
Hi Haze

The maths revision aids are good.

http://www.elevenplusexams.co.uk/pdf/Ma ... _Aid_2.pdf

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 Post subject: Posted: Fri Oct 23, 2009 3:20 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8113
ooo even better Mitasol - thanks for pointing that out...

we try calculating percentage etc when cutting pies up. even better calculate in terms of radians - cos then you can have so many Pi(e) radians..

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 Post subject: Posted: Fri Oct 23, 2009 3:30 pm

Joined: Thu Jan 22, 2009 7:57 pm
Posts: 156
And this is with 10 and 11 year old childeren? I didn't touch radians until maths A level!!!

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 Post subject: Posted: Fri Oct 23, 2009 4:19 pm

Joined: Mon Nov 24, 2008 1:25 pm
Posts: 2556
can't you just do, 10% of 32 would be 3.2, therefore 20% would be 6.4??

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 Post subject: Posted: Fri Oct 23, 2009 4:52 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8113
Haze wrote:
And this is with 10 and 11 year old childeren? I didn't touch radians until maths A level!!!

nah just messing about eating pizzas and pies at home... they know how to ask for a portion in radians... wouldn't be able to do owt else with them yet

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 Post subject: Posted: Fri Oct 23, 2009 4:53 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8113
Milla wrote:
can't you just do, 10% of 32 would be 3.2, therefore 20% would be 6.4??

don't think that works ...

10% of 32 = 32/10 - you are trying to calculate 20/32

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