Percentages Increase : GMAT Quantitative Section
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# Percentages Increase

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20 Jul 2013, 19:17
Please can anyone help me with my following query. I am very confused

Number x has increased by 100% ??
Number x has increased by a factor of 20 ??
Number x has decreased by a factor of 15??
Number x has an increase of 100% ??
Number x has increased to y ??
Number x has increased by y ??

What will be the value of x in each of above 6 cases.
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20 Jul 2013, 22:46
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Number x has increased by 100% ??
=> X as doubled 10->20
Number x has increased by a factor of 20 ??
=> x has increased by 1,2,4,5,10,20. I do not know if this is a percentage increase(+20%) or a multiplication(x20) or a sum(+20); I think that the latter should be correct.
Number x has decreased by a factor of 15??
=> x has decreased by 1,3,5,15, same as above
Number x has an increase of 100% ??
=> same as the first one
Number x has increased to y ??
=> example x=5, y=7; x has increased to y==> x=7
Number x has increased by y ??
=> example x=5, y=7; x has increased by y==> x=5+7=12

Hope this makes sense
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21 Jul 2013, 01:21
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Expert's post
Zarrolou wrote:
Number x has increased by 100% ??
=> X as doubled 10->20

Number x has increased by a factor of 20 ??
=> x has increased by 1,2,4,5,10,20. I do not know if this is a percentage increase(+20%) or a multiplication(x20) or a sum(+20); I think that the latter should be correct.

Number x has decreased by a factor of 15??
=> x has decreased by 1,3,5,15, same as above

Number x has an increase of 100% ??
=> same as the first one

Number x has increased to y ??
=> example x=5, y=7; x has increased to y==> x=7

Number x has increased by y ??
=> example x=5, y=7; x has increased by y==> x=5+7=12

Hope this makes sense

The red parts are not correct.

Increases by a factor of y means multiplied by y --> x increased by a factor of 20 --> result = 20x.

Decreased by a factor of y means divided by y --> x decreased by a factor of 15 --> result = x/15.

Hope it helps.
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21 Jul 2013, 20:50
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Expert's post
Responding to a pm:

How to resolve the following:

Number x has increased by 100% ??
Number x has increased by a factor of 20 ??
Number x has an increase of 100% ??
Number x has increased to y ??
Number x has increased by y ??

Solutions:

Number x has increased by 100%
x has increased by 100% of x i.e. x has become double of what it was originally.
If x was 10, it is now 20.

Number x has increased by a factor of 20
"increased by a factor of 20" means "multiplied by 20" (yes, kind of un-intuitive because I might expect it to INCREASE by 20x to become 21x but that is not the way it is used)
So x becomes 20x

Number x has an increase of 100% ??
Not usually used. We use "x has increased by 100%". It means x has becomes 2x.

Number x has increased to y ??
x has become y. Number of children (which has 5) has increased to 10 (now there are 10 children).

Number x has increased by y ??
y is added to x to give x + y. Number of children (which was 5) has increased by 10 (now there are 15 children).
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21 Jul 2013, 20:53
Merging similar topics.
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10 May 2016, 02:25
VeritasPrepKarishma

MAM LIKE YOUR WEIGHTED AVERAGE CONCEPT IN YOUR BLOG WHICH WAS OSSOM. HAVE YOU ALSO WRITTEN IN FOR PERCENTAGES CONCEPT AND FOR TIME AND WORK?? I WOULD LIKE TO READ THAT ALSO IF YOU HAVE WRITTEN
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13 May 2016, 06:05
Hi!

Number x has increased by a factor of 20 ??
Since 20 can have factors: 20, 1, 10, 2, 4, 5... why is it 20x and not 1x or 10x or 2x ... etc

Number x has decreased by a factor of 15??
Same question as above, why isn't it x/3 or x/5 etc..

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13 May 2016, 06:12
nk18967 wrote:
Hi!

Number x has increased by a factor of 20 ??
Since 20 can have factors: 20, 1, 10, 2, 4, 5... why is it 20x and not 1x or 10x or 2x ... etc

Number x has decreased by a factor of 15??
Same question as above, why isn't it x/3 or x/5 etc..

Hi,
Do not take literal meaning of FACTOR, here it means TIMES..
Number x has increased by a factor of 20 ?? MEANS X has increased 20 times
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13 May 2016, 06:14
chetan2u wrote:
nk18967 wrote:
Hi!

Number x has increased by a factor of 20 ??
Since 20 can have factors: 20, 1, 10, 2, 4, 5... why is it 20x and not 1x or 10x or 2x ... etc

Number x has decreased by a factor of 15??
Same question as above, why isn't it x/3 or x/5 etc..

Hi,
Do not take literal meaning of FACTOR, here it means TIMES..
Number x has increased by a factor of 20 ?? MEANS X has increased 20 times

Thank you! But how do we know when to take the literal meaning and when not to? Or for all questions like this, just assume it will be the number itself and not a 'factor' like the question says...
Re: Percentages Increase   [#permalink] 13 May 2016, 06:14
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