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List of EQUATIONS?

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List of EQUATIONS?

by gmatjedi » Sun May 16, 2010 3:07 pm
Has any member compiled and posted a list of EQUATIONS/PROCESSES that would be helpful in the Quant Section?
Below are listed a few interesting equations/processes that I came across.

1. Area of the triangle when coordinates of the vertices are (x1, y1), (x2, y2), (x3, y3)
= {|x1 (y2 - y3) + x2 (y3 - y1) + x3 (y1 - y2)|}/ 2
(from Rahul)

2. Generally, the smallest prime factor of h(n)+1 is larger than n/2.
(from cneal4 )

I hope each of us can share important formulas and/or processes that would enable solving the more difficult quant questions.

It could serve as a great resource for the community.
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by sanju09 » Mon May 17, 2010 12:31 am
gmatjedi wrote:Has any member compiled and posted a list of EQUATIONS/PROCESSES that would be helpful in the Quant Section?
Below are listed a few interesting equations/processes that I came across.

1. Area of the triangle when coordinates of the vertices are (x1, y1), (x2, y2), (x3, y3)
= {|x1 (y2 - y3) + x2 (y3 - y1) + x3 (y1 - y2)|}/ 2
(from Rahul)

2. Generally, the smallest prime factor of h(n)+1 is larger than n/2.
(from cneal4 )

I hope each of us can share important formulas and/or processes that would enable solving the more difficult quant questions.

It could serve as a great resource for the community.
Do you know that primes 41 and past are found by putting n = 1, 2, 3, 4, 5, ... in the prime function P (n) = n^2 - n + 41? But, it fails after some positive integer value of n. What is that n?
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by gmatjedi » Mon May 17, 2010 3:54 pm
thanks sanju.
not sure what the answer is.
how do you calculate it?

Another formula:
The Set Theory Formula to get the exact unique count in one set is :

P(A) + P(B) + P(C) - 2P(AnB) - 2P(AnC) - 2P(BnC) + 3P(AnBnC)
(from rn4 gmat)
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by sumanr84 » Mon May 17, 2010 8:27 pm
gmatjedi wrote:thanks sanju.
not sure what the answer is.
how do you calculate it?

Another formula:
The Set Theory Formula to get the exact unique count in one set is :

P(A) + P(B) + P(C) - 2P(AnB) - 2P(AnC) - 2P(BnC) + 3P(AnBnC)
(from rn4 gmat)
I think the above formula is not correct,
If you have 3 set such as A,B and C and you are told to find the total then you can apply the below formula,

Total = P(A) + P(B) + P(C) - 2P(AnB) - 2P(AnC) - 2P(BnC) + P(AnBnC) [ add the singles, subtract the doubles, and add back one triple]

Now to get unique count in one set you need to subtract from Total.
I am on a break !!
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