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

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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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01 May 2011, 07:42
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If 3^a * 4^b = c, what is the value of b?

(1) 5^a = 25
(2) c = 36
[Reveal] Spoiler: OA

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Re: what is the value of b? [#permalink]

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02 May 2011, 04:45
straight B. 36 = 2 ^2 * 3^2
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Re: what is the value of b? [#permalink]

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09 Nov 2011, 08:52
I'm going to go with B

36 = $$3^2 and 2^2$$

you are given that $$3^a*4^b=c$$

we can break down 4 to 2^2b
So now we have

$$3^a*2^2b=2^2*3^2$$

so a= 2, b = 2
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Re: what is the value of b? [#permalink]

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09 Nov 2011, 09:41
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a and b are not integers here.

consider this:

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

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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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13 Nov 2011, 09:20
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The question does not mention a and b to be Integers.
Individually,none of the statements suffice to reach the value of b.

Both the statements when used together,give the value of b.
3^2 * 4^b = 36.
b=1

Hence C.
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Re: what is the value of b? [#permalink]

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04 Feb 2012, 15:50
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amit2k9 wrote:
straight B. 36 = 2 ^2 * 3^2

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 non-integer $$a$$ 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.

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 Sep 2014, 23:42
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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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19 Jun 2015, 08:15
Hi Bunnel in the above explantion how can 3^a=36 be possible for any value a, it has to have an even no. plz clarify my doubt
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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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19 Jun 2015, 08:21
caster88 wrote:
Hi Bunnel in the above explantion how can 3^a=36 be possible for any value a, it has to have an even no. plz clarify my doubt

We are NOT told that a and b are integers. So, there exists some irrational a for which 3^a = 36: $$a= \frac{2 (log(2)+log(3))}{log(3)}\approx{3.2619}$$
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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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01 Nov 2016, 21:46
Hello from the GMAT Club BumpBot!

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Re: If 3^a * 4^b = c, what is the value of b? (1) 5^a = 25 (2) c   [#permalink] 01 Nov 2016, 21:46
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