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fractions and non-similar denominator.

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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fractions and non-similar denominator.

by mist3rh » Mon Jun 21, 2010 5:39 am
Okay -this is really sad that I am asking this question, I cannot remember a quicker way that i used back in school days to add fractions with different denominators. One question I am solving in the OG requires two fractions be added. That itself is not the answer or the purpose of the question, rather just one part of the question. And given there are only 2 minutes or so to solve the problem, this is going to be a nightmare if i dont find an easy way out.

So fraction being added is 1/15 + 1/18. Can anyone comment as to how this will be solved the quickest possible manner. 18*15 way of doing it is lengthy and would give a bigger multiple to struggle with.
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by amising6 » Mon Jun 21, 2010 5:50 am
mist3rh wrote:Okay -this is really sad that I am asking this question, I cannot remember a quicker way that i used back in school days to add fractions with different denominators. One question I am solving in the OG requires two fractions be added. That itself is not the answer or the purpose of the question, rather just one part of the question. And given there are only 2 minutes or so to solve the problem, this is going to be a nightmare if i dont find an easy way out.

So fraction being added is 1/15 + 1/18. Can anyone comment as to how this will be solved the quickest possible manner. 18*15 way of doing it is lengthy and would give a bigger multiple to struggle with.
dude only way yo u can do faster is find lcm do the normal way but try to speed up calculation
which you will have to develop with time

there is no shortcut to add fraction
even if there is one it will be very tough to get right answer go the traditional way
find lcm and do
wont take much time
Ideation without execution is delusion
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by intellijat » Mon Jun 21, 2010 6:37 am
mist3rh wrote:Okay -this is really sad that I am asking this question, I cannot remember a quicker way that i used back in school days to add fractions with different denominators. One question I am solving in the OG requires two fractions be added. That itself is not the answer or the purpose of the question, rather just one part of the question. And given there are only 2 minutes or so to solve the problem, this is going to be a nightmare if i dont find an easy way out.

So fraction being added is 1/15 + 1/18. Can anyone comment as to how this will be solved the quickest possible manner. 18*15 way of doing it is lengthy and would give a bigger multiple to struggle with.
hi......
as pointed by amising6 take the LCM route:
15=3*5
18=3*3*2
so lcm=3*3*2*5=90
or
15*18 can be easily multiplied as (10+5)*18=180+90=270
or
15*(20-2)=300-30=270
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by mist3rh » Mon Jun 21, 2010 6:46 am
Thanks guys...guess i may just have to become comfortable with having to calculate it like you mention. Quant questions are harder (in OG) than i thought- i wonder how those who manage to score 50 tend to get through these.
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