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GMAT prep quant! i need help

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GMAT prep quant! i need help [#permalink] New post 22 Dec 2009, 21:59
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DS Questions- (i got the answer but not sure how that is correct)
1. Are both x and y positive?
i) 2x-2y=1
ii)x/y>1
2. If n and y are both positive integers. 450y=n^3.
Which of the following must be an integer?
i) y/(3x2^2x5) ii) y/(3^2x2x5) iii) y/(3x2x5^2)
a) none
b) I only
c) II only
d) III only
e) I, II & III
3. x, y z are integers greater than 1, what is the value of x+y+z?
i) xyz=70
ii) x/yz=7/10
I am bit confused about the answers. please help me with the methods.
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Re: GMAT prep quant! i need help [#permalink] New post 22 Dec 2009, 23:36
Statement 1 can be verified by picking numbers. From the below table it is clear that Statement 1 is not sufficient.

x Y 2x-2y=1 x>0 & Y>0?
1 ½ 2-1=1 Yes
-1/2 -1 -1+2=1 No


Statement 2 can verified similarly with numbers. Statement 2 is not sufficient.
x Y x/y>1 x>0 & Y>0?
1 ½ 2 > 1 Yes
-1 -1/2 2>1 No




I think taken together also not sufficient.
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Re: GMAT prep quant! i need help [#permalink] New post 22 Dec 2009, 23:49
prasadrg wrote:
Statement 1 can be verified by picking numbers. From the below table it is clear that Statement 1 is not sufficient.

x Y 2x-2y=1 x>0 & Y>0?
1 ½ 2-1=1 Yes
-1/2 -1 -1+2=1 No


Statement 2 can verified similarly with numbers. Statement 2 is not sufficient.
x Y x/y>1 x>0 & Y>0?
1 ½ 2 > 1 Yes
-1 -1/2 2>1 No




I think taken together also not sufficient.


statement 1 and 2 alone are insuff but together they suffice

from statement1 we have x= (1 + 2y)/2 and from stmnt2 we have x/y >1 . Substituting value of x obtained in stmnt1 in stmnt 2 we have (1 + 2y)/2y > 1 ==> 1/2y + 1> 1 or 1/2y > 0 so y is +ve and for any +ve value of y x will also be +ve.

Hence C
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Re: GMAT prep quant! i need help [#permalink] New post 22 Dec 2009, 23:54
bidishabarpujari wrote:
3. x, y z are integers greater than 1, what is the value of x+y+z?
i) xyz=70
ii) x/yz=7/10
I am bit confused about the answers. please help me with the methods.


3. will go with A

i. xyz= 70 and all are >1 so only values satisfying this is 2*5*7 so we can find the value. hence suff
ii. x/yz = 7/10 ==> 10x = 7 yz => we can have a lot of possibilities here.
e.g.
x = 7 and y and z = 2 and 5
x= 70 and y and z can be (5,20) (10,10)
hence insuff
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Re: GMAT prep quant! i need help [#permalink] New post 23 Dec 2009, 00:03
bidishabarpujari wrote:
DS Questions- (i got the answer but not sure how that is correct)
2. If n and y are both positive integers. 450y=n^3.
Which of the following must be an integer?
i) y/(3x2^2x5) ii) y/(3^2x2x5) iii) y/(3x2x5^2)
a) none
b) I only
c) II only
d) III only
e) I, II & III


b) I only

On factorising 450 we get 2* 3^2 * 5^2
so we can write 450y = n^3 as 2* 3^2 * 5^2 y = n^3
Minimum value of y which will satisfy this equation will be 2^2*3*5

only option I y/ 2^2*3*5 will give an integer always
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Re: GMAT prep quant! i need help [#permalink] New post 23 Dec 2009, 08:07
Thanks you for your answers and especially the methods to get those answers.
The OA of Q1 is c, Q2 is b and Q3 is a.
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Re: GMAT prep quant! i need help [#permalink] New post 23 Dec 2009, 09:26
Thanks KP for clarifying.
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Re: GMAT prep quant! i need help [#permalink] New post 23 Dec 2009, 09:40
prasadrg wrote:
Thanks KP for clarifying.


anytime mate :)
Re: GMAT prep quant! i need help   [#permalink] 23 Dec 2009, 09:40
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