Gmat Plus 2

[msd_2008]

Q. Is ab = 1 ?

(1) aba = a

(2) bab = b


OA is E. Can someone explain?

Regards
MSD

[ronniecoleman]

IMO E is correct


1. a = 0 ab = 1

2. b = 0 , ab = 1

now both 1 & 2

ab = 1

or

a = 0 , b = 0

[rohangupta83]

IMO E is correct


1. a = 0 ab = 1

2. b = 0 , ab = 1

now both 1 & 2

ab = 1

or

a = 0 , b = 0

Ronnie

I still don't understand how your supposition that when a = 0, ab = 1 is possible.

[mental]

I) aba = a
aba - a =0
a(ab -1) = 0
a = 0, or ab = 1


II) bab = b
like I....... b=0 or ab=1

only one root common in both statements, ab=1

Ans should be C ?

[vishubn]

A)a^2b=a
b=a/a^2
b=a but cannot say if ab=1

B)same line a=b

together as well not sufficient

I think one has to remember even if u think this could be easily answered ( which i did intially ...but then i thought this cant be easy! some catch )

so eventually got the OA

OA E

[rohangupta83]

I) aba = a
aba - a =0
a(ab -1) = 0
a = 0, or ab = 1


II) bab = b
like I....... b=0 or ab=1

only one root common in both statements, ab=1

Ans should be C ?

Thanks for explaining the logic..

I agree with you regarding the OA.

using both equations we have a common solution so OA should be C

[GMATters1001]

I divided by 'a' in (1) and 'b' in statement (2) and got D. Then I realized that when you divide by a variable you potentially eliminate a solution (i.e. the variable could =0) which could be critical to a DS answer.

My thoughts on the responses above:
a=0 and b=0 aren't mutually exclusive! So a=0 and b=0 are possible common anwers.

There's two possibilities, that a=0 AND b=0 or that ab=1 that make both statements true i.e. ab could equal 1 or could equal 0. So C cannot be the correct answer.

IMO E

[muzali]

Could any of the math specialists please explain how to approach such a question?

stm1
aba = a
a(ab -1) = 0
a = 0, or ab = 1

stm2
Similar to stm1, b = 0, or ab = 1

Why cannot we derive ab=1 from both these statements and say answer is C?

[cramya]

Why cannot we derive ab=1 from both these statements and say answer is C?

Good question! I am not sure if this helps any but let me try.

Pick a=0 b=0 for stmt I and II. It is true

a=1 b=1 is also true. No where its mentioned that a and b are distinct so our consideration a=0 b=0 ; a=1 b=1 holds good.


ab=1 is true (redundant info from both statements since from either of the statements we can get this info)

I am sure others may be able to explain better also!

[logitech]

Q. Is ab = 1 ?

(1) aba = a

(2) bab = b


OA is E. Can someone explain?

Regards
MSD

This is a YES / NO question.

Is ab=1 ? YES IT IS - Sufficient , NO IT IS NOT = sufficient MAYBE = INSUF

St1 and St2 both have two solutions

St1+St2

a=0 & b =0

or AB=1 a=1/b

well...

ab can be 0 or ab=1

We are not sure...so MAYBE means E in yes/no DS question

Choose E

[muzali]

Q. Is ab = 1 ?

(1) aba = a

(2) bab = b


OA is E. Can someone explain?

Regards
MSD

This is a YES / NO question.

Is ab=1 ? YES IT IS - Sufficient , NO IT IS NOT = sufficient MAYBE = INSUF

St1 and St2 both have two solutions

St1+St2

a=0 & b =0

or AB=1 a=1/b

well...

ab can be 0 or ab=1

We are not sure...so MAYBE means E in yes/no DS question

Choose E

Logitech, if the question was similar to:

What is x: stm1: (x-1)(x-2)=0; stm2: (x-1)(x-3)=0

What would you choose?

[logitech]

Logitech, if the question was similar to:

What is x: stm1: (x-1)(x-2)=0; stm2: (x-1)(x-3)=0

What would you choose?

In this case I would choose C

Because it is not a YES or NO question and x=1 satisfies both equation. Am I right ?

[muzali]

I think Logitech is bang on...
"is ab=1" and "what is x" are indeed different question. Thanks for pointing this out.