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Re: number propreties [#permalink]
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03 May 2011, 01:02
considering a and b to be non integral values. a=1,2,3 b will have different values. Hence C is correct.
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Re: number propreties [#permalink]
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29 May 2011, 19:36
VeritasPrepKarishma wrote: kamalkicks wrote: If \(3^a4^b = c\), what is the value of b?
(1) \(5^a = 25\)
(2) c = 36
IS OA CORRECT!!
i will go by B, what do you say If you are wondering why stmnt 2 alone is not sufficient, think of it this way: \(3^a4^b = c\) (2) c = 36 So \(3^a4^b = 36\) Now for every value of a, there is a different value of b. Say, a = 1, then 4^b = 12 and b = 1.79 approx a = 2, then 4^b = 4 and b = 1 a = 3, then 4^b = 36/27 and b = 0.2 approx and so on... If we were given that a and b are integers, then answer would have been (B) If I solved the problem as: 3^a * 4^b = 36 3^a*2^2b = 3^2*2^2 [a = 2, b = 2] What is the problem? What is the difference between 3^a * 4^b = 36 and 5^21 x 4^11 =2x10^n
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Re: number propreties [#permalink]
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30 May 2011, 02:50
Baten80 wrote: VeritasPrepKarishma wrote: kamalkicks wrote: If \(3^a4^b = c\), what is the value of b?
(1) \(5^a = 25\)
(2) c = 36
IS OA CORRECT!!
i will go by B, what do you say If you are wondering why stmnt 2 alone is not sufficient, think of it this way: \(3^a4^b = c\) (2) c = 36 So \(3^a4^b = 36\) Now for every value of a, there is a different value of b. Say, a = 1, then 4^b = 12 and b = 1.79 approx a = 2, then 4^b = 4 and b = 1 a = 3, then 4^b = 36/27 and b = 0.2 approx and so on... If we were given that a and b are integers, then answer would have been (B) If I solved the problem as: 3^a * 4^b = 36 3^a*2^2b = 3^2*2^2 [a = 2, b = 2] What is the problem? What is the difference between 3^a * 4^b = 36 and 5^21 x 4^11 =2x10^n There is nothing wrong with the solution (a = 2, b = 1) except that it doesn't say that a and b are integers (as mentioned above) hence it is just one of the infinite solutions. a and b can be any real numbers and for every value of a, b will have a corresponding real value.
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Re: DS  value [#permalink]
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23 Sep 2011, 19:33
Ans:B
1). a =2 b,c=? Insufficient
2). 36 = 3^2x4^1 b =1 Sufficient



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Re: number propreties [#permalink]
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26 Sep 2011, 04:21
Quote: There is nothing wrong with the solution (a = 2, b = 1) except that it doesn't say that a and b are integers (as mentioned above) hence it is just one of the infinite solutions. a and b can be any real numbers and for every value of a, b will have a corresponding real value. Good point Karishma. We need to stop assuming the things we know
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Re: If 3^a*4^b = c, what is the value of b? (1) 5^a = 25 (2) c = [#permalink]
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29 Jan 2016, 08:29
Hi @Bunnel For option A, why is below logic wrong? Thanks in advance! 5^a = 25 => 5^a = 5^2 and because of this we can not really compare 5 as the base on both sides and get to conclusion that a = 2. Bunuel wrote: nusmavrik wrote: Q1 If 3^a*4^b = c, what is the value of b?
(1) 5^a = 25 (2) c = 36
If 3^a*4^b = c, what is the value of b?Note that we are not told that the variables are integers only. (1) 5^a = 25 > \(a=2\), but we can not get the values of \(b\). Not sufficient. (2) c = 36 > \(3^a*4^b = c\): it's tempting to write \(3^2*4^1=36\) and say that \(b=1\) but again we are not told that the variables are integers only. So, for example it can be that \(3^a=36\) for some noninteger \(a\) and \(b=0\), making \(4^b\) equal to 1 > \(3^a*4^b =36*1=36\). Not sufficient. (1)+(2) As \(a=2\) and \(c = 36\) then \(9*4^b=36\) > \(b=1\). Sufficient. Answer: C. Hope it's clear.



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Re: If 3^a*4^b = c, what is the value of b? (1) 5^a = 25 (2) c = [#permalink]
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30 Jan 2016, 01:45
neeraj609 wrote: Hi @Bunnel For option A, why is below logic wrong? Thanks in advance! 5^a = 25 => 5^a = 5^2 and because of this we can not really compare 5 as the base on both sides and get to conclusion that a = 2. Bunuel wrote: nusmavrik wrote: Q1 If 3^a*4^b = c, what is the value of b?
(1) 5^a = 25 (2) c = 36
If 3^a*4^b = c, what is the value of b?Note that we are not told that the variables are integers only. (1) 5^a = 25 > \(a=2\), but we can not get the values of \(b\). Not sufficient. (2) c = 36 > \(3^a*4^b = c\): it's tempting to write \(3^2*4^1=36\) and say that \(b=1\) but again we are not told that the variables are integers only. So, for example it can be that \(3^a=36\) for some noninteger \(a\) and \(b=0\), making \(4^b\) equal to 1 > \(3^a*4^b =36*1=36\). Not sufficient. (1)+(2) As \(a=2\) and \(c = 36\) then \(9*4^b=36\) > \(b=1\). Sufficient. Answer: C. Hope it's clear. But 5 = 5, isn't it?
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If 3^a*4^b = c, what is the value of b? (1) 5^a = 25 (2) c = [#permalink]
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27 Jun 2016, 02:42
@Karishima ,
A question.. Why not E?..
When checking A and B the the \(4^1\) can also be seen as \(2^2\)
So:
\(3^a*2^(2+b) = 2^2*3^2\) where 2^(2+b) is \(2^2*2^0\)
and we get that B can be 1 or 0.
Thanks!



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Re: If 3^a*4^b = c, what is the value of b? (1) 5^a = 25 (2) c = [#permalink]
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Re: If 3^a*4^b = c, what is the value of b? (1) 5^a = 25 (2) c =
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