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 Post subject: Nfer maths 11A Q47.Posted: Tue Aug 26, 2008 9:16 am

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 7138
Location: East Kent
Can anyone suggest a simple way of working teh question out. Mine is so long winded that I am sure it would take FAR too long in a test.

It's a pie chart of trees in a park

we know that 20% are beech
30% are Ash
8% are lime.

so 100 - 58 = 42% oak. (the missing information)

We also know 12 trees are lime

so 8% of total =12.

How many oak trees?

0.08 of total = 12

12/0.08 = x

once we have found x then we can go on to work out 42% of this.

The numbers are not easy to work with though and calcualtors aren't allowed. Am I missing something obvious.

My brain is just not functioning this week.

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 Post subject: Posted: Tue Aug 26, 2008 9:20 am

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
Hi,

If 8% is 12 then I would say 1% is 1.5

So 42% is 42 + 21 = 63

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 Post subject: Posted: Tue Aug 26, 2008 9:22 am

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 7138
Location: East Kent
Thanks .

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 Post subject: Posted: Wed Aug 27, 2008 8:11 am
I always say:
8% = 12
40%= 60
2% =1/4 of 12 = 3

42% = 63

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 Post subject: Posted: Wed Aug 27, 2008 8:20 am

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 7138
Location: East Kent
Thank you i was getting really bogged down in algebra and dividing by 0.08 while wondering how it could be done by a 10 year old without a calculator.

i'll note that down for future reference!

You will be pleased to know the brain has woken up a bit today...now if only I could touch type.......

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 Post subject: Posted: Wed Aug 27, 2008 9:46 am

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
fm - the unitary (or finding what 1 is) is a very powerful method and means you are not relying on 'nice' multiples ...

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 Post subject: mel xPosted: Wed Aug 27, 2008 12:17 pm

Joined: Thu Sep 14, 2006 7:32 pm
Posts: 410
Hi guest55

What do you think is the quickest way to work out devisions particularly when big numbers

DD is ok when deviding by 2 4 8 etc as you can half but panics when its odd numbers. As an example she had to work out

504 devided by 9

I showed her my way

_56___
9/504

9's into 50 = 5 r5 then 9's into 54 = 6 so answer = 56

Is this the quickest way?

Mel

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 Post subject: Posted: Wed Aug 27, 2008 12:29 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
Mel X,

Many teachers think that is not the best way to start learning division -

504 divided by 9 - estimate answer ... 500 divided by 10 - so about 50.

Has she understood chunking yet? My answer would depend how far she is is her 'preferred method'.

9 x 10 = 90

9 X 50 = 450

504 - 450 = 54

9 x 6 = 54 so the answer is 56.

When they use short division try to keep place value so say 9 into 500 ...

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 Post subject: Posted: Wed Aug 27, 2008 3:01 pm

Joined: Mon Jan 30, 2006 4:07 pm
Posts: 2668
Dear Guest55

Dear Mel

I teach My 11 plus childeren, the old fashioned way to divide, as you have laid out in your post. The understanding may not be the best, but it is by far the quickest method for the basic division required for the selection tests. As my children are proficient in their times tables [2 to 12 plus 13 and 15] divisions by these numbers are relatively easy.

They use this knowledge to divide: 9/504

If its 18s into 90, they take a good guess, then check their guess by multiplying back up.

I also teach the old fashioned way of multiplying.

I tell the children that although they can use my method for 11 plus, they must revert to their teachers methods for their numeracy lessons....

Patricia

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 Post subject: Posted: Wed Aug 27, 2008 3:09 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
You can join those on the naughty step Patricia

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