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M18-31

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M18-31  [#permalink]

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New post 16 Sep 2014, 01:04
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

88% (00:40) correct 12% (01:18) wrong based on 190 sessions

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New post 16 Sep 2014, 01:04
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New post 20 Jun 2015, 01:05
how u take lcm and add plz elaborate?
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New post 20 Jun 2015, 02:15
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New post 07 Aug 2016, 12:14
How did you divide the MMC by the factors?
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New post 22 Apr 2017, 06:31
Please can one disclose how the common denominator has been divided by the independent denominators
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New post 27 May 2017, 21:27
Hi wwambugu14,

Not sure if I understand you right. But Bunuel has simply added the two fractions.

The Common Denominator would be the LCM of \(\sqrt{2}\) and \((2 + \sqrt{2})\). This would be the multiplication of the two. This turns out as - \(\sqrt{2}(2 + \sqrt{2})=\sqrt{2}*2 + \sqrt{2}*\sqrt{2}=\sqrt{2}*2+2\)

Once the Common denominator is set as the LCM its pretty much addition as we do with fractions. in the end, both Numerator and denominator end up to be \(\sqrt{2}*2+2\) and we get one as the answer.

See the official solution for how its actually done.

Hope this helps.


wwambugu14 wrote:
Please can one disclose how the common denominator has been divided by the independent denominators

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New post 13 Jul 2017, 06:33
I can´t crack the algebra, can someone please help or tell me where can I learn more? I tried to look for examples but I did not find any.
Thanks
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New post 13 Jul 2017, 07:03
1
cocojiz wrote:
I can´t crack the algebra, can someone please help or tell me where can I learn more? I tried to look for examples but I did not find any.
Thanks

Multiple and divide first expression by \(\sqrt{2}\) and second expression by \(2-\sqrt{2}\) and use \((a+b)(a-b)=a^2 -
b^2\) for second expression's denominator.
What we will get is :
\(\sqrt{2}/2\) + (2- \(\sqrt{2}\)) / (4-2 )

that becomes:
(\(\sqrt{2} + 2 - \sqrt{2}\))/2
= 2/2
=1
=B

You can read more in GMATClub Maths book chapter Ratio and Proportions and "Algebraic Identities" from chapter Algebra.

Hope this helped :)
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New post 14 Jul 2017, 03:52
When stuck with MCM, estimation work as well:

> 1/sqrt(2) ~ 1/1,41 ~ 1/1,5 ~ 2/3

> 1/(2+sqrt(2)) ~ 1/(3,41) ~ 1/3,3 ~ 1/3

> 2/3 + 1/3 = 1

Note that I rounded one up and one down.
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Re: M18-31   [#permalink] 14 Jul 2017, 03:52
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