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If (3^a)*(4^b)=c , then what is the value of b? 1. 5^a=25 2. [#permalink ]
18 Jun 2006, 04:14

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If (3^a)*(4^b)=c , then what is the value of b?

1. 5^a=25

2. c=36

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GMATT73 on 18 Jun 2006, 15:07, edited 1 time in total.

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shobhitb wrote:

straight B for me

Can you please illustrate how you got that answer?

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GMATT73 wrote:

shobhitb wrote:

straight B for me

Can you please illustrate how you got that answer?

Statement 1

a=2 but no value of b so cannot determine c

Statement 2

c is given!

So sufficient

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(B) was my guess too, but according to the OA we are both wrong.

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what is the source of this problem, Matt?!!

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GMATT73 wrote:

If (3^a)*(4^b)=c , then what is the value of c? 1. 5^a=25 2. c=36

maybe some typo?

I guess if it is not B than it should be D.C is out cause 2st alone is sufficient

So How did they get the valuse of C from 1st?

All we can get from

5^a=25 is that a=2

9*4^b=c defenitely not suff

Matt but the question was what is the value of C ))) I knew there was a typo))

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Yurik79 on 19 Jun 2006, 08:41, edited 1 time in total.

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Matt,

It doesn't seem right. It probably has to be something like (C < 36) or ( C > 36) or something else. I mean, if it says C = 36, then (B) certainly qualifies.

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Here`s the problem in source format.

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GMATT73,

Can you post the

Kaplan explanation for this.

Are there any fraction values of a/b that can also yield 36.

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St1:
No information about c. Insufficient.
St2:
c = 36, (3^a)(4^b) = c
Can be 9*4 --> a = 2, b = 1.
I'll go with B. I can't think of any other combination that works.

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Well, I suppose since the stem didn't say a and b are integers, we really can't say that a=

2 and b=1 if c=36. For example, a could equal to (ln4/ln3+2) and b could equal to 0. (I had chosen B too, and looks like it IS wrong.)

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Last edited by

HongHu on 19 Jun 2006, 07:28, edited 1 time in total.

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sgrover wrote:

GMATT73,

Can you post the

Kaplan explanation for this.

Are there any fraction values of a/b that can also yield 36.

Here is the OE from

Kaplan . Not that it helps much...

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The correct answer is C (also in

Kaplan as the link provided by you)

If (3^a)*(4^b)=c , then what is the value of b?

1. 5^a=25

2. c=36

1. 5^a= 25 --> a= 2 , nothing about c ---> insuff

2. nothing about a --> insuff

1 and 2:

a=2 ---> 3^a = 9, we have c=36 ---> 4^b = 36/9= 4 --> b=1

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laxieqv wrote:

The correct answer is C (also in

Kaplan as the link provided by you)

If (3^a)*(4^b)=c , then what is the value of b?

1. 5^a=25

2. c=36

1. 5^a= 25 --> a= 2 , nothing about c ---> insuff

2. nothing about a --> insuff

1 and 2:

a=2 ---> 3^a = 9, we have c=36 ---> 4^b = 36/9= 4 --> b=1

Here`s where I get a little hazy....

If (3^a)*(4^b)=36, then doesn`t b have to equal 1?

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GMATT73 wrote:

laxieqv wrote:

The correct answer is C (also in

Kaplan as the link provided by you)

If (3^a)*(4^b)=c , then what is the value of b?

1. 5^a=25

2. c=36

1. 5^a= 25 --> a= 2 , nothing about c ---> insuff

2. nothing about a --> insuff

1 and 2:

a=2 ---> 3^a = 9, we have c=36 ---> 4^b = 36/9= 4 --> b=1

Here`s where I get a little hazy....

If (3^a)*(4^b)=36, then doesn`t b have to equal 1?

if we know only c ..it's impossible to conclude that b=1 coz a and b are not necessarily integers

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laxieqv wrote:

GMATT73 wrote:

laxieqv wrote:

The correct answer is C (also in

Kaplan as the link provided by you)

If (3^a)*(4^b)=c , then what is the value of b?

1. 5^a=25

2. c=36

1. 5^a= 25 --> a= 2 , nothing about c ---> insuff

2. nothing about a --> insuff

1 and 2:

a=2 ---> 3^a = 9, we have c=36 ---> 4^b = 36/9= 4 --> b=1

Here`s where I get a little hazy....

If (3^a)*(4^b)=36, then doesn`t b have to equal 1?

if we know only c ..it's impossible to conclude that b=1 coz a and b are not necessarily integers

DUH!

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laxieqv wrote:

GMATT73 wrote:

laxieqv wrote:

The correct answer is C (also in

Kaplan as the link provided by you)

If (3^a)*(4^b)=c , then what is the value of b?

1. 5^a=25

2. c=36

1. 5^a= 25 --> a= 2 , nothing about c ---> insuff

2. nothing about a --> insuff

1 and 2:

a=2 ---> 3^a = 9, we have c=36 ---> 4^b = 36/9= 4 --> b=1

Here`s where I get a little hazy....

If (3^a)*(4^b)=36, then doesn`t b have to equal 1?

if we know only c ..it's impossible to conclude that b=1 coz a and b are not necessarily integers

I still have a problem in agreeing with this reasoning. If a,b are not integers, how can lets say 3^1.25 * 4^3.45 equals an integer value?

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Guess I am way late to post for this.. but here goes
S1 :
5^a = 25 = 5^2
=> a = 2
=Don't know c
=> Not sufficient.
S2: c = 36
Don't know a; Not sufficient.
S1&S2:
a =2, c =36 => b = 1
Sufficient : Answer C

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sridhars wrote:

I still have a problem in agreeing with this reasoning. If a,b are not integers, how can lets say 3^1.25 * 4^3.45 equals an integer value?

How about my example?

Quote:

a could equal to (ln4/ln3+2) and b could equal to 0.

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the answer is B. There is no power of 3 that will yield 36

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