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## Difficult GMAT Math Problems

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pg850 Rising GMAT Star
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Sun Jul 05, 2009 9:13 am
hey Eric, I was wondering if you could tell me where these qs are from? I plan to do the MGMAT tests and if these qs are from the same pool I dont want to solve them now and then know what the answers are when I m doing the tests..

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nikhilvinci Just gettin' started!
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Wed Jul 15, 2009 4:52 am
hi
can someone please mail me the collection of tough math problems .i am not able to download it
my email id is nikhilvinci@gmail.com
thankyou

Jake Blues Just gettin' started!
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Thu Jul 23, 2009 2:18 am
Quote:
hey Eric, I was wondering if you could tell me where these qs are from? I plan to do the MGMAT tests and if these qs are from the same pool I dont want to solve them now and then know what the answers are when I m doing the tests..
Fellas,any idea about that? I'm in the same situation,just do not want to spoil my CAT experience in case these questions are taken from CAT's pool.
Can anybody shed the light on the origin of these questions?

busybee1 Just gettin' started!
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Wed Jul 29, 2009 8:20 am
Hi All,

I believe you are right tohellandback.
For this question the answer shld be 159 or the question shld be stating 79*80 to be the sum of first n even numbers.

-----------------------------------------------
are you sure the answers are correct..I did the first problem and I think it is done wrong

1. The sum of the even numbers between 1 and n is 79*80, where n is an odd number, then n=?
Sol: First term a=2, common difference d=2 since even number

therefore sum to first n numbers of Arithmetic progression would be

n/2(2a+(n-1)d)

= n/2(2*2+(n-1)*2)=n(n+1) and this is equal to 79*80

therefore n=79 which is odd...
now the n here is the number of terms in the series 2,4,6..
the real n being asked in the question should be 79*2+1=159

charlesdiss Just gettin' started!
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Fri Feb 05, 2010 12:54 am
I thought on the GMAT we didn't need to memorize formulas? Looking at the first problems it seems that I needed to have the formulas for arthimetic progressions memorized. Any thoughts?

jeffedwards Really wants to Beat The GMAT!
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Fri Feb 05, 2010 1:24 pm
Thanks so much for posting this. Awesome! I've been looking for difficult questions....on a budget

guillermogallicc Just gettin' started!
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Tue May 18, 2010 10:10 am
your right man, just came to the same conclusion..159

TheCloakedMonk Just gettin' started!
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Wed Sep 01, 2010 1:32 pm
I have a much better approach for question #3. (The current explanation is confusing to me)

You can look at this as and "OR" problem.

If a leap year happens every 4 years, then a person has a 1/4 chance of being born in that year because he/she can only possibly be born in 1 out of the 4 given years.

Therefore, the probability of a person being born out of the four given years is 1/4 = 25%. Therefore the probability the person A "OR" person B was born {P(A or B)} in the leap year is 1/4 + 1/4 = 2/4 = 50%.

The question asks for the number of people that would yield a greater than >50% probability. Therefore, since 2 people yields 50%, 3 people are needed to surpass 50%. There is a 75% chance {1/4 + 1/4 +1/4} that one of three people {P(A or B or C)} was born in the leap year.

Am I correct or have I just gotten lucky?

Enjoy!

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TheCloakedMonk Just gettin' started!
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Wed Sep 01, 2010 1:55 pm
Question #1

The easiest way to do this is:

Sum of Numbers = (#of Numbers)(Middle Number)
Sum of Even Numbers {Where n is odd...like in this problem} = ((n-1)/2)*((n-1)/2+1) = 79*80
Therefore, 79 = (n-1)/2, so n = 159

What you must see:
# of Even Numbers = (n-1)/2 = 79
Middle # = (n-1)/2 +1 = 80

You can easily devise this because the only difference between the two terms is "+1" which is obviously 80 NOT 79.

Hope that clears the slate.

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boysangur Just gettin' started!
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Tue Sep 07, 2010 11:25 pm
Man, this problem set got me very concerned. Are there really some problems like these on the actual GMAT? Some of them are not very hard but, although it is subjective, some seem a little too hard. Even looking at the solutions, some of them are pretty darn complex and lengthy. Like the solution to number 11 is given as follows:

Since 12w=3x=4y,

w=3:12=1:4 and x:y=4:3

so, w = 1
x = 4
y = 3

the fractional part of the square is shaded:
{(w+x)^2 - [(1/2)wx + (1/2)wx +(1/2)xy + (1/2)w(2w)]}/(w+x)^2

= {(w+x)^2 - [wx + (1/2)xy + w^2)]}/[(w+x)^2]

=[(5^2) -(4+6+1)]/(5^2)

= (25 - 11)/25

= 14/25

I mean, really, there is no way I could figure this out and solve it in anywhere near 2 minutes. I thought I was getting close to the finish line in my math review, as I solved most of the OG 12 problems easily but now I'm really discouraged.

Tani GMAT Titan
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Wed Sep 15, 2010 9:38 am
Looks to me as though the answer to the first problem is wrong.

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ecmpec Just gettin' started!
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Mon Oct 25, 2010 7:27 am
Can any one mail me the the file along with answers at rahul.mechies@gmail.com?

Tani GMAT Titan
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Mon Oct 25, 2010 8:01 am
Re: leap year problem (#3).

If you add the probabilities that a single person would be born in a leap year (1/4), then with four people you would have a 100% possibility that one would be born in leap year. But, clearly all four could have been born in the same, non-leap year, so the possibility is not 100%. The explanation that came with the problem is correct.

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Tani Wolff

rohitkalla Just gettin' started!
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Sun Jul 10, 2011 9:11 pm
Can somebody please mail the math tough questions doc to me ? it's not opening in my system..

bpositive09@gmail.com.

Thanks.

dev.gavande Rising GMAT Star
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Mon Sep 12, 2011 10:20 pm
Thanks!!!

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