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Shortcut Method 4 Multiple Increase or decrease percentage!!

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Shortcut Method 4 Multiple Increase or decrease percentage!! [#permalink] New post 08 Sep 2010, 12:26
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HI Guys.
I found a good method while going thru a book in case u guys dont know!!!

suppose a questions says first the price of an article increase by 20% then after that price got reduced by 5%
normally we calculate seprately for some original price
like say
(1.2)x and then to calculate 5 % reduce we calculate 5% of (1.2)x

shortcut is we can calculate by formula (p1+/-p2)+/-((p1*p2)/100)
p1-->1st percentage
p2 -->2nd one
sign of + or - in first bracket depending on increase or decrease
in second bracket sign outside it will be product of initial sign of p1 and p2 like for both decrease +ve*-ve=-ve
i know u may find it difficult to cram but see an example u dont need to learn at all

sol for above eg

20-5-((20*5)/100)
15-1
14% of original value

another example
suppose length increase by 20% breadth by 30 % then overal area increase wil be 20+30+(20*30)/100)=56% more of original
..
we use -ve sign for reduction ,+ve for increase and if both are decrease then in product of p1*p2 part value will be +ve (since -ve*-ve=+ve)


Hope it help u guys..!!
thanx
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Re: Shortcut Method 4 Multiple Increase or decrease percentage!! [#permalink] New post 08 Sep 2010, 14:37
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I think I'm just lazy to try to memorize another formula. There are just way too many formulas in this world, so why not just try to solve by deriving things (or just use common sense)?

20% increase, then 5% decrease, is simply:
(1.2y)*(.95) = 1.14y (or 14% increase). What's so difficult with that?

or if you do: 7% increase, then 30% decrease, and then 15% increase:
(1.07)*(0.70)*(1.15) ~ 0.86y (or 14% decrease)
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Re: Shortcut Method 4 Multiple Increase or decrease percentage!! [#permalink] New post 08 Sep 2010, 21:41
adalfu wrote:
I think I'm just lazy to try to memorize another formula. There are just way too many formulas in this world, so why not just try to solve by deriving things (or just use common sense)?

20% increase, then 5% decrease, is simply:
(1.2y)*(.95) = 1.14y (or 14% increase). What's so difficult with that?

or if you do: 7% increase, then 30% decrease, and then 15% increase:
(1.07)*(0.70)*(1.15) ~ 0.86y (or 14% decrease)


Hi adalfu well said it depends on person to person for u it may be easy to do calculation in mind like adding .2 subtracting .05 and then multiplying 1.2 with .95(for me its bit difficult & time consuming though to multiply 1.2 with .95)........ for others it may not be the case....
one can simply deal with the given values by just using it...!! :)
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Re: Shortcut Method 4 Multiple Increase or decrease percentage!! [#permalink] New post 09 Sep 2010, 00:54
I think this method is also pretty neat !
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Re: Shortcut Method 4 Multiple Increase or decrease percentage!! [#permalink] New post 23 Apr 2012, 08:48
This is a great shortcut,

so for

Inc inc (p1+p2)
pos*po =+ so + is sign outside second brackets

Inc decr (p1-p2)
pos*neg = - so - is sign outside second brackets

decr decr (-p1--p2) which is same as -p1+p2
neg*neg = + so + is sign outside second brackets

decr inc (-p1+p2)
neg*pos = - so - is sign outside second brackets

is this correct?
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Re: Shortcut Method 4 Multiple Increase or decrease percentage!! [#permalink] New post 27 Apr 2012, 19:08
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Yes, it is certainly a good approach in some cases. I have discussed the derivation and application of this formula in this post.
http://www.veritasprep.com/blog/2011/02 ... e-changes/
I have also discussed the cases where you might want to use it.
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Re: Shortcut Method 4 Multiple Increase or decrease percentage!!   [#permalink] 27 Apr 2012, 19:08
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Shortcut Method 4 Multiple Increase or decrease percentage!!

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