Cancelling down fractions using prime factorising

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kal12003
Posts: 169
Joined: Thu Mar 06, 2014 2:50 pm

Cancelling down fractions using prime factorising

Post by kal12003 »

Cancel 296
➖
37

Can anyone please explain the answer for 296/37 fraction. DD is struggling.


Thanks in advance
Proud_Dad
Posts: 500
Joined: Fri Oct 11, 2013 9:55 am

Re: Cancelling down fractions using prime factorising

Post by Proud_Dad »

The answer is just 8.

Unless I'm not understanding the question properly?
kal12003
Posts: 169
Joined: Thu Mar 06, 2014 2:50 pm

Re: Cancelling down fractions using prime factorising

Post by kal12003 »

I thought that however dd seems to have an longwinded way of having to show working out.
Eg. 6/15 =
6 - 3x2 = 2
15 - 5x3 =5

So the answer is 3/5

Maybe it's the fact that the question involves bigger numbers that's frazzled her :/
ToadMum
Posts: 11908
Joined: Wed Jan 18, 2012 12:41 pm
Location: Essex

Re: Cancelling down fractions using prime factorising

Post by ToadMum »

Start really simply? What the question is asking is essentially, how many times does 37 go into 296, with the possibility of there being a remainder. Add 37 to 37, then add another 37... Stop when the last 37 you add takes you over 296 - or in this case, when you get to 296, as it is a multiple of 37.

Or am I missing something as well?
Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read.Groucho Marx
Guest55
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Joined: Mon Feb 12, 2007 2:21 pm

Re: Cancelling down fractions using prime factorising

Post by Guest55 »

It looks like they are being expected to break down the numbers into their prime factors.

37 is a prime number so you are looking to break down the numerator:

296 = 2 x 148 = 2 x 2 x 74 = 2 x 2 x 2 x 37
kal12003
Posts: 169
Joined: Thu Mar 06, 2014 2:50 pm

Re: Cancelling down fractions using prime factorising

Post by kal12003 »

Apologies as I clearly haven't explained it very well.
Guest55 - that's exactly what she's been asked to do. She's managed it fine with simpler questions however this one has really thrown her. As her answer she has put
296/37 =38x8 =8
=37x1 = 1
=8

Would the bottom working out be simply 37x1 as 37 is the lowest prime number here?
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: Cancelling down fractions using prime factorising

Post by Guest55 »

I think I write the numerator as I did and leave the denominator as 37 is prime.

2 x 2 x 2 x 37
37
kal12003
Posts: 169
Joined: Thu Mar 06, 2014 2:50 pm

Re: Cancelling down fractions using prime factorising

Post by kal12003 »

Guest55 - May I ask if, in your opinion, this is age appropriate for lower set year 7. Am rather concerned dd is struggling with it so much.
ToadMum
Posts: 11908
Joined: Wed Jan 18, 2012 12:41 pm
Location: Essex

Re: Cancelling down fractions using prime factorising

Post by ToadMum »

kal12003 wrote:Apologies as I clearly haven't explained it very well.
Guest55 - that's exactly what she's been asked to do. She's managed it fine with simpler questions however this one has really thrown her. As her answer she has put
296/37 =38x8 =8
=37x1 = 1
=8

Would the bottom working out be simply 37x1 as 37 is the lowest prime number here?
(Guest55, please rescue me here ?) Where does the 38 come from?
Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read.Groucho Marx
kal12003
Posts: 169
Joined: Thu Mar 06, 2014 2:50 pm

Re: Cancelling down fractions using prime factorising

Post by kal12003 »

Toadmum - I apologise, that was a typing error on my part & should have read 37 as opposed to 38. Sorry for any confusion, it really has been one of those days!
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