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 Post subject: Maths Q help please
PostPosted: Tue Sep 25, 2018 9:40 am 
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Joined: Wed Feb 28, 2018 10:05 pm
Posts: 59
Hi All,

My DD is in year 6 and she is struggling with a particular maths question.

Normally I can help her without any problems but I am looking for an easier way to solve the problem below.

We usually complete these by finding the LCM and making the denominator the same and adjusting the numerator.

The whole of her Maths table struggled with this and teacher came to help and said the LCM is 840 and they could then continue but it does seem odd for a Yr 6 q.

Amy help on how to solve this type of problem quicker when the LCM is a high number.

Q. Arrange these in ascending order

2/6, 1/5, 2/7, 1/4


Thank you.


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 9:48 am 
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Joined: Sun Sep 22, 2013 7:17 am
Posts: 19
Try making numerators same.
1/5, 1/4, 1/3.5, 1/3


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 10:09 am 
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Joined: Tue Mar 18, 2014 9:35 pm
Posts: 70
PoppyPup wrote:
Hi All,

My DD is in year 6 and she is struggling with a particular maths question.

Normally I can help her without any problems but I am looking for an easier way to solve the problem below.

We usually complete these by finding the LCM and making the denominator the same and adjusting the numerator.

The whole of her Maths table struggled with this and teacher came to help and said the LCM is 840 and they could then continue but it does seem odd for a Yr 6 q.

Amy help on how to solve this type of problem quicker when the LCM is a high number.

Q. Arrange these in ascending order

2/6, 1/5, 2/7, 1/4


Thank you.

Make denominator same, to do this find LCM of 6,5,7,4. LCM is 420, not 840. Once denominator is same, you can compare numerator and put accordingly in
OR
you can convert fraction into decimals and compare. This is more easier way if child find difficulties in LCM.


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 10:21 am 
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Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
schalla wrote:
Try making numerators same.
1/5, 1/4, 1/3.5, 1/3

No - fractions cannot have decimal denominators.


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 10:40 am 
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Joined: Sat Oct 01, 2016 6:02 pm
Posts: 1186
That is true but if you're just being asked to arrange them in order of size I think it's a useful way of approaching the question. Far quicker than multiplying all the numerators up to the LCD.


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 10:45 am 
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Joined: Sun Sep 22, 2013 7:17 am
Posts: 19
It is easy to make numerators same some times.
If you want to be precise find LCM of numerators which is 2.
It makes 2/10, 2/8, 2/7, 2/6


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 10:50 am 
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Joined: Fri Aug 24, 2018 5:26 pm
Posts: 125
There are two ways of comparing fraction - one by comparing fraction with like denominators and another by comparing fraction with like numerators.

First method involves finding LCM for denominators (240 in this case), finding equivalent fractions with new denominators and arranging numerators.

Second method - the same, but for numerators. LCM for numerators in this case is 2. Equivalent fractions - 2/10, 2/8, 2/7, 2/6. The higher denominators is, the smaller is value.

And of course, converting everything to decimals is working method as well, but not in this case as there is 6 and especially 7 in denominator, what will give us recurring decimals...


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 12:38 pm 
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Joined: Fri Mar 10, 2017 5:06 pm
Posts: 682
Agree that making the numerators the same is a far simpler (and therefore better) method in this example.

I'm surprised that the teacher didn't suggest this and instead advised them to find the LCM which makes it much more tricky.


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 2:28 pm 
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Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
Mathematically, making the numerator the sane is not a good approach - it leads to errors and is not advised. I would NEVER suggest it so please don't tell children to do this.

In this question, simplifying the 2/6 to 1/3 means you can order three of them easily
2/6 = 1/3, 1/5, 2/7, 1/4
1/5, 1/4, 1/3 so all we need to decide is where 2/7 goes which make it much easier


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 Post subject: Re: Maths Q help please
PostPosted: Tue Sep 25, 2018 3:04 pm 
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Joined: Wed Sep 02, 2015 10:56 am
Posts: 283
Surferfish wrote:
I'm surprised that the teacher didn't suggest this and instead advised them to find the LCM which makes it much more tricky.

Blame the NC. It's all about equivalent fractions in KS2. Pity the neglected numerator :)

The point of the question was probably to demonstrate the use of prime factors. You don't just 'stumble' onto a LCM of 240 :o


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