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 Post subject: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 3:53 pm

Joined: Mon Mar 08, 2010 1:03 pm
Posts: 1413
Hello,

When DS has been ordering decimals or fractions, he's been taught to change them all to the same denominator (for fractions), or put them in tenths, hundredths columns etc (for decimals). However, neither he, nor I , can find a way to get some 'commonality' (ie the same denominator, or turning into decimals) for the following fraction/ decimal mix (WITHOUT using a calculator). Can anyone help? And, can anyone tell me if this mix would appear in an 11+ GS exam?

0.85, 4/5, 5/8

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 3:59 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8542
I guess I'd say that 4/5 is 8/10 so is 0.8, and that 1/8 is 0.125 (worth learning by heart) so 5/8 is 0.625 - then it is straightforward. I think also one might just have a "feel" for 5/8 being less than 8/10 --- it just "looks" closer to one half.

I would have thought that could be a GL assessment maths question.

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 4:02 pm

Joined: Sat Dec 03, 2011 3:14 pm
Posts: 688
4 divided by 5 gives a decimal answer of 0.8 and 1 divided by 8 would give you 0.125.

You can use long division or 'bus stop' methods to change fractions to decimals

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 4:04 pm

Joined: Mon Mar 08, 2010 1:03 pm
Posts: 1413
Ahem ... seems obvious now ... Thanks Mystery and Leanmeamum!

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 4:46 pm

Joined: Fri Oct 11, 2013 8:55 am
Posts: 500
mystery wrote:
I guess I'd say that 4/5 is 8/10 so is 0.8, and that 1/8 is 0.125 (worth learning by heart) so 5/8 is 0.625 - then it is straightforward. I think also one might just have a "feel" for 5/8 being less than 8/10 --- it just "looks" closer to one half.

I would have thought that could be a GL assessment maths question.

One way to get a feel of 5/8, is to think that 6/8 = 3/4 = 0.75.

So 5/8 < 0.75, so must be the smallest.

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 5:09 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
You only need to change them into the same denominator if you cannot judge their size or position on a number line in relation to each other.

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 5:52 pm

Joined: Mon Mar 08, 2010 1:03 pm
Posts: 1413
Guest55 wrote:
You only need to change them into the same denominator if you cannot judge their size or position on a number line in relation to each other.

DS doesn't seem to be able to do this. Which particular fraction sizes should he know off by heart? 1/4, 1/2, 3/4, various eighths, sixteenths?

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 6:28 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
Once you can order quarters then eight should be simple and sixteenths ...

Look at a fraction wall it can help some children 'see' the fractions in order.

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 6:38 pm

Joined: Thu Oct 18, 2012 9:41 am
Posts: 444
Think it's worthwhile memorizing the usual 1/2 , 1/4 , 3/4 as Guest55 says eights and sixteenths can be worked out, so other ones to memorise IMO are

1/3, 1/8 (meaning that you can work out sixths too if need be)

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 Post subject: Re: Ascending order mix of decimals and fractionsPosted: Tue Feb 04, 2014 9:51 pm

Joined: Mon Sep 10, 2012 8:44 pm
Posts: 65
Probably not the best way to do this example, but if you wanted to get the same denominator (i.e. 40), I would do the following:

0.85 = 85/100 = 17/20 = 34/40

4/5 = 32/40

5/8 = 25/40

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