The value of B ?

Expert replies

avik.ch: Legendary Member; Posts: 641; Joined: Wed Apr 20, 2011 1:15 amFollowed by: 32 members; Thanked: 149 times; GMAT Score:760

by avik.ch » Mon Sep 17, 2012 12:04 am

If 3^a4^b = c, what is the value of b?

(1) 5a = 25

(2) c = 36

OA = C

I think the second statement is sufficient.

Source : Kaplan

Like this post

Source: Beat The GMAT — Data Sufficiency | Mon Sep 17, 2012 12:04 am

everything's eventual: Master | Next Rank: 500 Posts; Posts: 101; Joined: Sun Jun 03, 2012 10:10 pmFollowed by: 1 member; Thanked: 10 times

by everything's eventual » Mon Sep 17, 2012 2:25 am

hmmm..I am not sure how you did it...but this was my method :

Statement 1) is def not sufficient.

Statement 2) says c = 36 = 3^2 * 2^2

Equating both sides we get (5^4)^b = 2

Then we get b = 0 and 2) should be sufficient.

Like this post

vk_vinayak: Legendary Member; Posts: 502; Joined: Tue Jun 03, 2008 11:36 pmFollowed by: 21 members; Thanked: 99 times

by vk_vinayak » Mon Sep 17, 2012 2:47 am

avik.ch wrote:If 3^a4^b = c, what is the value of b?

(1) 5a = 25

(2) c = 36

OA = C

I think the second statement is sufficient.

Source : Kaplan

1) Tells us about only a. INSUF

2) (3^a) * (4^b) = 36 = (3^2) * (4^1) => b=1. SUF.

- VK

I will (Learn. Recognize. Apply)

Like this post

avik.ch: Legendary Member; Posts: 641; Joined: Wed Apr 20, 2011 1:15 amFollowed by: 32 members; Thanked: 149 times; GMAT Score:760

by avik.ch » Mon Sep 17, 2012 2:57 am

So we can reasonably conclude that the OA is wrong.

Thanks !!

Like this post

avik.ch: Legendary Member; Posts: 641; Joined: Wed Apr 20, 2011 1:15 amFollowed by: 32 members; Thanked: 149 times; GMAT Score:760

by avik.ch » Mon Sep 17, 2012 2:59 am

everything's eventual wrote:
Statement 2) says c = 36 = 3^2 * 2^2

Equating both sides we get (5^4)^b = 2

Then we get b = 0 and 2) should be sufficient.

I am not sure how you are getting b=0 ?? Can you please elaborate !!

Like this post

vk_vinayak: Legendary Member; Posts: 502; Joined: Tue Jun 03, 2008 11:36 pmFollowed by: 21 members; Thanked: 99 times

by vk_vinayak » Mon Sep 17, 2012 3:20 am

avik.ch wrote:So we can reasonably conclude that the OA is wrong.

Thanks !!

I searched for this question, and found that OA is technically correct, but the question is incomplete. Refer Stewart's explanation at: https://www.beatthegmat.com/a-data-from- ... 81048.html

B is the logical answer.

- VK

I will (Learn. Recognize. Apply)

Like this post

imskpwr: Master | Next Rank: 500 Posts; Posts: 377; Joined: Wed Sep 14, 2011 10:45 amFollowed by: 1 member; Thanked: 10 times

by imskpwr » Mon Sep 17, 2012 6:05 am

avik.ch wrote:If 3^a4^b = c, what is the value of b?

(1) 5a = 25

(2) c = 36

OA = C

I think the second statement is sufficient.

Source : Kaplan

At first, I was a bit skeptical as we don't know anything about the RANGE of a and b, but now i am sure now that it's a trick q.

I mean a and b could be integers or non integers; rationals or irrationals;etc.

But once we know that a=2(integer), we can say Definitely that b has to be an integer to satisfy the equation(3^a4^b = c) for c=36.

Hence, BOTH STATEMENTS ARE REQUIRED TO ANSWER.
From 2, we cannot deduce that a and b are only "whole numbers". There may be other values which can satisfy the equation....this would be easier if you think of a solution where a and b are not whole numbers.

This must be a VERY HIGH LEVEL Q.....probably when one is in 50s....and when you are at that level you don't get peanuts so beware of such qs at that level.
I don't think GMAT ask such qs, But Indian CAT do throw such q at you.

Like this post

everything's eventual: Master | Next Rank: 500 Posts; Posts: 101; Joined: Sun Jun 03, 2012 10:10 pmFollowed by: 1 member; Thanked: 10 times

by everything's eventual » Mon Sep 17, 2012 5:44 pm

everything's eventual wrote:
Statement 2) says c = 36 = 3^2 * 2^2

Equating both sides we get (5^4)^b = 2

Then we get b = 0 and 2) should be sufficient.

I am not sure how you are getting b=0 ?? Can you please elaborate !!

Hello, I messed up the whole question. Sorry. I had a brain freeze.

First of all I understood the question as follows :

[3 ^ (a^4)]^ b = c

Statement 2) says c = 36 = 3^2 * 2^2

So comparing original equation and value of C, we get (a^4)^b = 2

Now we cannot solve the above equation unless we know the value of a. From statement 1) we get a= 5.

Therefore, (5^4)^b = 2 and so b = 0.

So yes, according to my flawed explanation the answer is C.

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review