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If x and y are integers and 2 < x < y, does y = 16 ?

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Archit143
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If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   09 Mar 2013, 13:06
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If x and y are integers and 2 < x < y, does y = 16 ?

(1) The GCF of X and Y is 2.
(2) The LCM of X and Y is 48.
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C
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Re: If x and y are integers and 2 < x < y, does y = 16? [#permalink] New post   06 Nov 2013, 19:05
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accincognito wrote:
If x and y are integers and 2 < x < y, does y = 16?

(1) The GCF of x and y is 2
(2) The LCM of x and y is 48

Dear accincognito,
I'm happy to help. :-)

This is a hard problem! See this post for some insight:
https://magoosh.com/gmat/2012/gmat-math-factors/

Statement #1: The GCF of x and y is 2
This leave open a wide array of possibilities. All we know is that x and y are two even numbers, both bigger than 2, with no common factors other than two: they could be
x = 4, y = 6
x = 6, y = 8
x = 6, y = 10
x = 6, y = 16
So, it's possible for y to equal 16 or equal something else. This statement, alone and by itself, does not give us sufficient information, so it is insufficient.

Statement #2: The LCM of x and y is 48
Without any other information, we could have
x = 3, y = 16
x = 4, y = 48
So, it's possible for y to equal 16 or equal something else. This statement, alone and by itself, does not give us sufficient information, so it is insufficient.

Combined: this is where it gets interesting.
The GCF of x and y is 2
The LCM of x and y is 48
This is a tricky combination. First, let's list all the factors of 48 --- in order to have a LCM of 48 with another number, each number must be a factor of 48.
factors of 48 = {1, 2, 3, 4, 6, 8, 12, 16, 24, 48}
Those are the possible candidates for x & y. We can eliminate 1 & 2, because x > 2, and we can eliminate 3, because that cannot have a GCF of 2 with anything else.
Possibilities for x & y = {4, 6, 8, 12, 16, 24, 48}
If y = 48, then every other number in the set is factor of 48, so the GCF would be the smaller number --- e.g. the GCF of 6 and 48 is 6. Therefore, we can't use 48.
If y = 24, then the first four numbers are factors of 24, so they don't work, and the GCF of 16 & 24 is 8. Therefore, we can't use 24.
Possibilities for x & y = {4, 6, 8, 12, 16}
Suppose y = 16
x = 4, y = 16 ===> GCF = 4, doesn't work
x = 6, y = 16 ===> GCF = 2 --- this is one possible pair!!
x = 8, y = 16 ===> GCF = 8, doesn't work
x = 12, y = 16 ===> GCF = 4, doesn't work
Suppose y = 8
x = 4, y = 8 ===> GCF = 4, doesn't work
x = 6, y = 8 ===> GCF = 2, but LCM = 24, doesn't work
Suppose y = 6
x = 4, y = 6 ===> GCF = 2, but LCM = 12, doesn't work
So, after all that, the only pair that satisfies both statements is x = 6, y = 16, so it turns out, y does in fact equal 16. We are able to give a definitive answer to the prompt question, so the combined statements are sufficient.

Answer = (C)

Does all this make sense?
Mike :-)
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   01 Apr 2014, 20:57
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Archit143 wrote:
If x and y are integers and 2 < x < y, does y = 16 ?

(1) The GCF of X and Y is 2.
(2) The LCM of X and Y is 48.


Given: 2 < X < Y
Question: Does Y = 16?

(1) The GCF of X and Y is 2.
X = 2a; Y = 2b (a and b are co prime integers)
Y may or may not be 16 e.g. X = 6, Y = 16 OR X = 6, Y = 8 etc

(2) The LCM of X and Y is 48.
\(48 = 2^4 * 3\)
One of X and Y must have 2^4 = 16 as a factor and one must have 3 as a factor. Again, Y may or may not be 16 e.g. X = 6, Y = 16 OR X = 1, Y = 48 etc

Using both together, X = 2a, Y = 2b.
Since a and b need to be co-prime and both X and Y need to be greater than 2, one of a and b must be 3 and the other must be 8 (since X and Y already have a 2 to make 16).
X = 6, Y = 16 (since X is less than Y).
Y must be 16.

Answer (C)
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Re: if x and y are integers and 2<x<y, does y =16 [#permalink] New post   19 Oct 2013, 20:07
Archit143 wrote:
I know that each statements are insufficient by itself. But i think Even taken together they are insufficient.
We know that GCF*LCM = X*Y
So X*Y = 96
Hence , when y = 24 , x =4
Similarly when y = 16 , x = 6
So i think both statements are insufficient taken together.

Archit


If GCF is 2 and LCM is 48, than the Pair of X and Y can be:
X=2,Y=48 and X=6,Y=16 and X=16, Y=6 and X=48, Y=2

I think the answer is
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Re: if x and y are integers and 2<x<y, does y =16 [#permalink] New post   20 Oct 2013, 04:36
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suk1234 wrote:
Archit143 wrote:
I know that each statements are insufficient by itself. But i think Even taken together they are insufficient.
We know that GCF*LCM = X*Y
So X*Y = 96
Hence , when y = 24 , x =4
Similarly when y = 16 , x = 6
So i think both statements are insufficient taken together.

Archit


If GCF is 2 and LCM is 48, than the Pair of X and Y can be:
X=2,Y=48 and X=6,Y=16 and X=16, Y=6 and X=48, Y=2

I think the answer is
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E


Please read the stem carefully. It's given that 2<x<y.
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   05 Nov 2013, 03:15
I am not getting the right answer for some reason. Can you please tell me the set of numbers for which both the statements are satisfied?

thank you.
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   05 Nov 2013, 07:00
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emailmkarthik wrote:
If x and y are integers and 2 < x < y, does y = 16 ?

(1) The GCF of X and Y is 2.
(2) The LCM of X and Y is 48.

I am not getting the right answer for some reason. Can you please tell me the set of numbers for which both the statements are satisfied?

thank you.


x = 6 and y = 16 --> the greatest common factor of 6 and 16 is 2, and the least common multiple of 6 and 16 is 48.
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Re: If x and y are integers and 2 < x < y, does y = 16? [#permalink] New post   Updated on: 29 May 2014, 07:18
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Again @Mike, No need for all the fuzz, let's see

x,y are positive integers and 2<x<y. Is y=16?

First statement
GCF (x,y) is 2

Well we could have:

x=4, y=6 answer is NO or x=6, y=16 answer is YES

Hence insufficient

Second Statement
LCM (x,y) is 48
48 = 2^4 * 3

Now we can test cases here too: Either x=3 and y=2^4 when answer is YES
OR x=7 y = 48 answer is NO

Both together
Since GCF =2 and LCM = 48 and since 2<x<y we can only have x=6, y=16

Hence C is the correct answer
Please ask if anything remains unclear
Cheers
J :)

Originally posted by jlgdr on 31 Mar 2014, 08:20.
Last edited by jlgdr on 29 May 2014, 07:18, edited 1 time in total.
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   11 Jan 2016, 17:52
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Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.


If x and y are integers and 2 < x < y, does y = 16 ?

(1) The GCF of X and Y is 2.
(2) The LCM of X and Y is 48.

In the original condition, there are 2 variables(x,y) and 1 equation(2<x<y), which should match with the number of equations. So you need 1 more equation. For 1) 1 equation, for 2) 1equation, which is likely to make D the answer.
For 1), (x,y)=(4,6) -> no, (x,y)=(6,16) -> yes, which is not sufficient.
For 2), (x,y)=(3,48) -> no, (x,y)=(6,16) -> yes, which is not sufficient.
When 1) & 2), (x,y)=(6,16) -> yes, which is sufficient. Therefore, the answer is C.


 For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   18 Aug 2017, 18:10
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When I see GCD, I think, "the most they have in common." When I see LCM, I think, "the least you need to make all of them." Helps me, maybe it can help someone else.

Statement 1: Insufficient, lots of number greater than 2 have a GCD of 2: 8 and 6 for instance or 16 and 14.

Statement 2: LCM of x and y is 48, which is (2^5)*3. This is also going to be insufficient. You want to think of different combinations of those prime factors. For instance, we can have x = 3 and y = 32. Can we have anything else (remember the only stipulation is that x<y)? x = 6 and y = 16. These give us two different answers.

Together:

There are only two examples from the second statement that are possible: x = 6, y = 16 and x = 3, y = 32. Because 3 and 32 don't have a common factor of 2, we can exclude that case and we are left with x = 6, y = 16 and the answer is 'yes'.

Sufficient --> C
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If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   26 Nov 2018, 19:51
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Archit143 wrote:
If x and y are integers and 2 < x < y, does y = 16 ?

(1) The GCF of X and Y is 2.
(2) The LCM of X and Y is 48.

\(2 < x < y\,\,{\text{ints}}\)

\(y\,\,\mathop = \limits^? \,\,16 = {2^4}\)


\(\left( 1 \right)\,\,GCF\left( {x,y} \right) = 2\,\,\,\left\{ \begin{gathered}\\
\,{\text{Take}}\,\,\left( {x,y} \right) = \left( {{2^2},2 \cdot 3} \right)\,\,\, \Rightarrow \,\,\,\left\langle {{\text{No}}} \right\rangle \hfill \\\\
\,{\text{Take}}\,\,\left( {x,y} \right) = \left( {2 \cdot {{3,2}^4}} \right)\,\,\, \Rightarrow \,\,\,\left\langle {{\text{Yes}}} \right\rangle \hfill \\ \\
\end{gathered} \right.\)


\(\left( 2 \right)\,\,LCM\left( {x,y} \right) = {2^4} \cdot 3\,\,\,\left\{ \begin{gathered}\\
\,\left( {\operatorname{Re} } \right){\text{Take}}\,\,\left( {x,y} \right) = \left( {2 \cdot {{3,2}^4}} \right)\,\,\, \Rightarrow \,\,\,\left\langle {{\text{Yes}}} \right\rangle \hfill \\\\
\,{\text{Take}}\,\,\left( {x,y} \right) = \left( {{2^2}{{,2}^4} \cdot 3} \right)\,\,\, \Rightarrow \,\,\,\left\langle {{\text{No}}} \right\rangle \hfill \\ \\
\end{gathered} \right.\)


\(\left( {1 + 2} \right)\,\,\,\left\{ \begin{gathered}\\
\,\left( 1 \right) \cap \left( 2 \right)\,\,\,\, \Rightarrow \,\,\,\,xy = GCF\left( {x,y} \right) \cdot LCM\left( {x,y} \right) = 3 \cdot {2^5}\,\,\,\left( * \right) \hfill \\\\
\,\left( 1 \right)\,\, \Rightarrow \left\{ \begin{gathered}\\
x = 2 \cdot M \hfill \\\\
y = 2 \cdot N \hfill \\ \\
\end{gathered} \right.\,\,\,\,\,GCF\left( {M,N} \right) = 1\,\,,\,\,\left( * \right)\,\, \Rightarrow \,\,3 \cdot {2^3} = MN\,\,\,\,\left( {M,N \geqslant 2} \right) \hfill \\\\
\left( {M,N} \right) = \left( {{2^3},3} \right)\,\,\, \Rightarrow \,\,\,\left( {x,y} \right) = \left( {{2^4},2 \cdot 3} \right)\,\,\, \Rightarrow \,\,\,x > y\,\,{\text{impossible}} \hfill \\\\
\therefore \left( {M,N} \right) = \left( {{{3,2}^3}} \right)\,\,\, \Rightarrow \,\,\,\left( {x,y} \right) = \left( {2 \cdot {{3,2}^4}} \right)\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\left\langle {{\text{Yes}}} \right\rangle \hfill \\ \\
\end{gathered} \right.\)


This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   26 Nov 2018, 19:58
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grassmonkey wrote:
When I see GCD, I think, "the most they have in common." When I see LCM, I think, "the least you need to make [satisfy] all of them." Helps me, maybe it can help someone else.

Excellent, grassmonkey. This is essentially what is going on. (I prefer the "satisfy" expression - I mentioned it in red- , but the meaning is the same.)

You got a kudos of mine for this observation!

Congrats and success in your studies,
Fabio.
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Re: If x and y are integers and 2 < x < y, does y = 16 ? [#permalink] New post   04 Oct 2023, 09:38
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