Percentages

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Haze
Posts: 156
Joined: Thu Jan 22, 2009 8:57 pm

Percentages

Post by Haze »

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! :?
mm2
Posts: 247
Joined: Fri Jan 25, 2008 9:36 pm
Location: moseley

Post by mm2 »

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
hermanmunster
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Post by hermanmunster »

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%
Haze
Posts: 156
Joined: Thu Jan 22, 2009 8:57 pm

Post by Haze »

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 :)
mitasol
Posts: 2756
Joined: Wed Feb 27, 2008 9:59 am

Post by mitasol »

Hi Haze

The maths revision aids are good.

http://www.elevenplusexams.co.uk/pdf/Ma ... _Aid_2.pdf
hermanmunster
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Location: The Seaside

Post by hermanmunster »

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..
Haze
Posts: 156
Joined: Thu Jan 22, 2009 8:57 pm

Post by Haze »

And this is with 10 and 11 year old childeren? I didn't touch radians until maths A level!!! :shock:
Milla
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Joined: Mon Nov 24, 2008 2:25 pm

Post by Milla »

can't you just do, 10% of 32 would be 3.2, therefore 20% would be 6.4??
hermanmunster
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Location: The Seaside

Post by hermanmunster »

Haze wrote:And this is with 10 and 11 year old childeren? I didn't touch radians until maths A level!!! :shock:
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
hermanmunster
Posts: 12818
Joined: Fri Sep 15, 2006 9:51 am
Location: The Seaside

Post by hermanmunster »

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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