Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized for You
we will pick new questions that match your level based on your Timer History
Track Your Progress
every week, we’ll send you an estimated GMAT score based on your performance
Practice Pays
we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Re: If 3^a * 4^b = c, what is the value of b? (1) 5^a = 25 (2) c
[#permalink]
Show Tags
04 Feb 2012, 15:50
4
6
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.
Re: If 3^a * 4^b = c, what is the value of b? (1) 5^a = 25 (2) c
[#permalink]
Show Tags
09 Nov 2011, 09:41
1
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
Re: If 3^a * 4^b = c, what is the value of b? (1) 5^a = 25 (2) c
[#permalink]
Show Tags
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: \(a= \frac{2 (log(2)+log(3))}{log(3)}\approx{3.2619}\)
_________________
close
43% (01:15) correct 
