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PostPosted: Wed Nov 20, 2013 11:49 am 
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Can anyone tell me if any questions on converting cl to l or mg to g or kg have ever come up in an 11+ exam. DS has never brought home questions with such small units before and I wondered if they were used in the 11+ or if it's just his school stretching his class?

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PostPosted: Wed Nov 20, 2013 12:01 pm 
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Only someone with a stock of old Kent maths 11plus papers could tell you - I don't have that!!

It's worth doing though. Your school sounds more thorough in year 5 than ours. It's easy too - but it's a good test of your child's accuracy and their memory for how many of these various things there are in something else. Going to do this to my year 5 child sometime! The thing they have never done is imperial to metric and vice versa. This does come up according to a relative who did it a few years back.


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PostPosted: Wed Nov 20, 2013 12:04 pm 
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I'm slightly blanching at it because it's not something I'm terribly good with. I can objectively see it's easy, but I can never remember how many 10s, 100s or 1000s I'm supposed to multiply or divide by and get totally confused. I've tried looking for a conversion table for all these measurements but can never find it all in one place.

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PostPosted: Wed Nov 20, 2013 12:42 pm 
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Hi fatbananas,

Look up the maths revision aid number 1 and number 6 on this website as they both have a useful list of these terms and whether they are 1/10, 1/100 etc. I've printed all of these revision aids off for my reference more than anything, as I like you start to get confused about how many zeros there should or shouldn't be! :lol:


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PostPosted: Wed Nov 20, 2013 12:44 pm 
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Prefixes for metric units:

m = milli = thousandths
c = centi = hundredths
d = deci = tenths (not commonly used)
k = kilo = thousands
M = Mega = Millions

http://en.wikipedia.org/wiki/Metric_prefixes


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PostPosted: Wed Nov 20, 2013 12:48 pm 
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11+ or not, it's useful to know.
I used an imaginary unit to explain to DD.
Let's call it a wibble. Because it's funny so it helps remember.

100 centiwibbles in a wibble. The clue is in the centi bit
1000 milliwibbles in a wibble. Again clue in the milli bit
1000 wibbles in a kilowibble.
1000000 wibbles in a Megawibble. Think mega millions.

Most people don't need much more than that, either smaller or larger, but if yo want more le me know.

Coincidently I've just had to tell one of our grad engineers off for using centmetres. Stiffly speaking cm is not an SI unit.


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PostPosted: Wed Nov 20, 2013 1:34 pm 
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Yes, thanks everyone. I think the thing DS and I found tricky was things like writing 4,500,000mm in km. Do you have to change the mm into m first before you can then convert into km? Or is there another, quicker, way of doing it?

Another one was 250mg into kg.

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PostPosted: Wed Nov 20, 2013 1:35 pm 
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Its fairly straightforward for most basic measurements like length (metres) and mass (kg).

It can get a bit confusing for areas and volumes though.

Note that there are 10,000 square cm in a square metre because being squared units its 100 x 100. Children quite often make the mistake of thinking that there are just 100 square cm in a square metre though (understandably).

With volumes its even more confusing because they can be measured in either litres/millilitres or cubic metres/cubic centimetres.

There are 1000 millilitres in a litre as you would expect.

But there are a million cubic centimetres in a cubic metre (100 x 100 x 100).

Also, 1 cubic centimetre (or cc) is the same volume as 1 millilitre. So there are a thousand cubic centimetres in a litre.

Finally 1 litre of water weighs exactly 1kg, which is sometimes useful to know.

(The above stuff about areas and volumes probably won't be required for 11+ though, so don't bother trying to teach it to your child unless it specifically comes up, as it will likely just confuse them!)


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PostPosted: Wed Nov 20, 2013 1:44 pm 
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fatbananas wrote:
Yes, thanks everyone. I think the thing DS and I found tricky was things like writing 4,500,000mm in km. Do you have to change the mm into m first before you can then convert into km? Or is there another, quicker, way of doing it?

Another one was 250mg into kg.

If it's easier to do it in steps fine. Possibly less likely to make errors


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PostPosted: Wed Nov 20, 2013 1:45 pm 
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fatbananas wrote:
Yes, thanks everyone. I think the thing DS and I found tricky was things like writing 4,500,000mm in km. Do you have to change the mm into m first before you can then convert into km? Or is there another, quicker, way of doing it?

Another one was 250mg into kg.


The safest way is probably to convert first from mm to m and then m to km. Its quite quick because you just divide by 1000 to get the metres and then divide by 1000 again to get the km.

i.e. 4,500,000mm = 4,500 m = 4.5km.

Simliarly 250mg = 0.25g = 0.00025kg.

Its also worth them bearing in mind what the different units actually represent in real life. i.e. a km is a long distance, while a mm is a short distance. So there will be lots and lots of little mm in a single km. This allows you to check that the final answer looks reasonable. If it doesn't you've probably multiplied when you shoulkd have divided or vice versa.


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