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Is 4^(x+y)=8^(10) ? [#permalink]
 18 Sep 2012, 03:19
Question Stats:
53% (01:50) correct
46% (00:57) wrong based on 4 sessions
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
18 Sep 2012, 03:20
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
18 Sep 2012, 05:20
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Is 4^{x+y}=8^{10} ? (1) x - y = 9 (2) y/x = 1/4 4^{x+y}=8^{10} ---> 2^2{x+y}=2^3{10}-----> 2^{x+y}=2^{15}The question can be restated as Is x+y = 15? 1) x-y = 9 --->Since x & y can assume any value---->Insufficient 2) x= 4y ---> No Absolute value is given for x & y, Only ratio is given-----> Insufficient 1+2) 4y-y = 9 ----> 3y=9---->Sufficient Thus Answer C
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
18 Sep 2012, 06:49
Bunuel wrote:
Is 4^{x+y}=8^{10} ?
(1) x - y = 9
(2) y/x = 1/4
the given eqn can be solved as: 2^2(x+y) = 2^3(10) => x+y = 15 Stmt 1) x - y = 9 can take many values for x and y and satisfy the eqn Stmt 2) y/x = 1/4, here also x and y can take many values combining both 1) and 2) the eqn can be solved to get values of x and y and can be verified if these x and y satisfies the given eqn Hence C
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
18 Sep 2012, 10:13
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Bunuel wrote: The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions ProjectIs 4^{x+y}=8^{10} ? (1) x - y = 9 (2) y/x = 1/4 Practice Questions
Question: 41
Page: 278
Difficulty: 600 GMAT Club is introducing a new project: The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you! From the question is X + Y = 15? 1st Option X - Y = 9 it can be any thing and any no. not necessarly the nos whose sum is equal to 15. Not Sufficient. 2nd Option: Y/x = 1/4 again Y and X can be any thing not necessarly the nos. whose summ is equal to 15. Not sufficient. Combining Both options: X - X/4 = 9 X = 12 therefore Y = 3. so Answer is "C". If my explaination you like kindly give one KUDOS
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
18 Sep 2012, 10:17
first i calculated E... then after luking at above solution..i wud say..its C..
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
20 Sep 2012, 00:39
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The question is simply is x + y = 15?
All we need is to know the value of the sum of x and y to get sufficiency.
(1) x -y= 9
10 - 1 is 9
11 - 2 is 9
24 - 9 is 15
INSUFFICIENT
(2) y/x = 1/4 or 4y = x many possibilities , INSUFFICENT
X - y = 9
(4y) - Y = 9
y = 3
x = 12
answer: c
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
21 Sep 2012, 03:46
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
21 Sep 2012, 03:57
Ans:C
4^(x+y)=8^(10)
=>2^2(x+y)=2^3(10)
=>x+y=15?
Statement1:x-y=9----Insufficent
Statement2:y/x=1/4=>x=4y---Insufficent
By combining St1&st2
y=3 and x=12 which gives x+y=15---Sufficient
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
03 Mar 2013, 22:21
Hi, could you please help clarify? I'm a little bit confused.
Isn't the answer D?
(1) X-Y=9 ----> X=9+Y
We can just put "X=Y+9" in the initial equation X+Y=15 to solve the equation without any help from the 2nd equation, y/x = 1/4.
The same goes to the second equation
(2) y/x = 1/4 -------> X=4Y
Just put substitute the X in the initial equation, X+Y=15, with the 4Y and then solve the equation for both X and Y.
So, we can actually get the answer using only 1 of statement. So why is the answer C.
Billion thanks in advance!
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
04 Mar 2013, 03:27
wutthiyo wrote: Hi, could you please help clarify? I'm a little bit confused.
Isn't the answer D?
(1) X-Y=9 ----> X=9+Y
We can just put "X=Y+9" in the initial equation X+Y=15 to solve the equation without any help from the 2nd equation, y/x = 1/4.
The same goes to the second equation
(2) y/x = 1/4 -------> X=4Y
Just put substitute the X in the initial equation, X+Y=15, with the 4Y and then solve the equation for both X and Y.
So, we can actually get the answer using only 1 of statement. So why is the answer C.
Billion thanks in advance! Welcome to GMAT Club! Actually the correct answer is C, not D. From the stem the question became: is x + y = 15? Now, (2) says that x - y = 9. Can we tell from this whether x + y = 15? No! Consider x = 10 and y = 1 for a NO answer and x = 12 and y = 3 for an YES answer. Hence, the first statement is NOT sufficient. The same for the second statement. The problem with your solution is that you assumed that we have two equations for each statement, whereas we have just one: x - y = 9 for (1) and y/x = 1/4 for (2). The second equation, x + y = 15 is not given to be true, we are asked to find whether it's true. Hope it's clear.
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
05 Mar 2013, 23:50
Bunuel wrote:
Welcome to GMAT Club!
Actually the correct answer is C, not D.
From the stem the question became: is x + y = 15?
Now, (2) says that x - y = 9. Can we tell from this whether x + y = 15? No! Consider x = 10 and y = 1 for a NO answer and x = 12 and y = 3 for an YES answer. Hence, the first statement is NOT sufficient.
The same for the second statement.
The problem with your solution is that you assumed that we have two equations for each statement, whereas we have just one: x - y = 9 for (1) and y/x = 1/4 for (2). The second equation, x + y = 15 is not given to be true, we are asked to find whether it's true.
Hope it's clear.
Oh! Thanks a lot! That's clear. So when a question ask whether an equation is true or not, we cannot use it in solving the problem. Am I right? ^___^
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Re: Is 4^(x+y)=8^(10) ? [#permalink]
06 Mar 2013, 02:35
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wutthiyo wrote: Bunuel wrote:
Welcome to GMAT Club!
Actually the correct answer is C, not D.
From the stem the question became: is x + y = 15?
Now, (2) says that x - y = 9. Can we tell from this whether x + y = 15? No! Consider x = 10 and y = 1 for a NO answer and x = 12 and y = 3 for an YES answer. Hence, the first statement is NOT sufficient.
The same for the second statement.
The problem with your solution is that you assumed that we have two equations for each statement, whereas we have just one: x - y = 9 for (1) and y/x = 1/4 for (2). The second equation, x + y = 15 is not given to be true, we are asked to find whether it's true.
Hope it's clear.
Oh! Thanks a lot! That's clear. So when a question ask whether an equation is true or not, we cannot use it in solving the problem. Am I right? ^___^ Yes, you cannot use it as a given.
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PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!
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Re: Is 4^(x+y)=8^(10) ?
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06 Mar 2013, 02:35
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