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# x, y, a, and b are four positive integers. D is the greatest common

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x, y, a, and b are four positive integers. D is the greatest common  [#permalink]

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19 Sep 2016, 04:36
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55% (hard)

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59% (01:37) correct 41% (01:56) wrong based on 94 sessions

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x, y, a, and b are four positive integers. D is the greatest common divisor of x and y. Is D > 20?

(1) x = 10a + 20b

(2) y = 20a + 40b

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Re: x, y, a, and b are four positive integers. D is the greatest common  [#permalink]

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19 Sep 2016, 05:11
1
Bunuel wrote:
x, y, a, and b are four positive integers. D is the greatest common divisor of x and y. Is D > 20?

(1) x = 10a + 20b

(2) y = 20a + 40b

We are clearly given that x, y, a, and b are four positive integer

Stat 1: lets sub a = 1 and b = 1 , we get x as 10+20 = 30...Not sure about y...Insufficient. ( we can't take a or b as 0, because 0 is neither positive or negative)

Stat 2: y = 60..not sure about x value..Insufficient.

Both : 30 and 60 are the numbers and GCD is 30...Sufficient.

IMO option C.
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Re: x, y, a, and b are four positive integers. D is the greatest common  [#permalink]

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19 Sep 2016, 05:18
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I think E, since we don't know about a and b

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Re: x, y, a, and b are four positive integers. D is the greatest common  [#permalink]

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19 Sep 2016, 06:20
3
Bunuel wrote:
x, y, a, and b are four positive integers. D is the greatest common divisor of x and y. Is D > 20?

(1) x = 10a + 20b

(2) y = 20a + 40b

St : 1 only talks about x ...(insufficient)
St : 2 only talks about y...(insufficient)

St 1+2 : y = 20a + 40b = 2(10a+20b) = 2x
Therefore, y = 2x
So, the GCD of x & y = x
Now, we are gibing that a & b are positive integers...
so minimum value of x = 10(1) + 20(1) = 30..
So D = 30 > 20.

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Re: x, y, a, and b are four positive integers. D is the greatest common  [#permalink]

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19 Sep 2016, 13:41
Yes, you are right. I mistakenly thought d is gcd of X,y,a and b. That's why I will never do well in GMAT

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Re: x, y, a, and b are four positive integers. D is the greatest common  [#permalink]

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06 Aug 2019, 00:51
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Re: x, y, a, and b are four positive integers. D is the greatest common   [#permalink] 06 Aug 2019, 00:51