Is A*B even?

Here is what i did in this Question =>
We need to see if A*B is even or not.
Notice we aren't told whether they are integers or not.
Statement 1->
A+B=7
A=2
B=5
AB=Even
A=2.3
B=4.7
AB≠Even
Hence not sufficient

Statement 2=>
B is even
If A = integer => AB will be even
But we got no info on A
Hence not sufficient

Combing the two statements =>A=integer -integer = integer
Hence A and B are both integers

Hence AB must be even

Hence C
_________________

Hi,

This is a perfect example for trap question in GMAT.

Already someone has figured the trap.

Answer choice B would have been the obvious trap answer. Whenever anything look too obvious it’s better to cross check, may not every time it would be a trap answer, but it’s always better to have a another look at it.

I will give my 2 – cents to this question.

Question: Is A*B is even?

That is product of two numbers is it even?

Note that we don’t know anything about A and B,

These below three rules of addition and multiplication of integers will help.

Add or sub :

Even + even = Even

Even + Odd = Odd

Odd + Odd = Even

Multiplication:

Odd * odd = odd

Even * odd = even

Even * even = even.

So let’s get into the statements,

Statement I is insufficient:

A + B = 7

First of all here A + B is 7, with this we can’t really say whether A and B are integers,

Maybe here,

A = 3.5 and B = 3.5

Or it could be

A= 3 and B = 4.

So insufficient.

Statement II is insufficient.

B is even,

Here is where someone has to careful because it’s easy to fall for the trap here, because B is even then AB is even.

Note that: This is possible only when A and B is even.

We can get that B is an integer, but not really sure about A.

It could be,

A = ½ and B = 2, answer to the question would be NO.

Or

A = ½ and B = 4, Answer to the question would be YES.

Together it is sufficient,

A+B = 7,

Since B is even, A has to be odd to get the sum as odd integer.

So AB is even.

So together it is sufficient.

Answer is C.

Hope this helps
_________________

More than 50 sessions (timer attempts)
39 percent hit rate.
I hope that answers your question.

Apart form that -> There is no other way to justify the difficulty level of any non official question.


Regards
Stone Cold
_________________

Each alone is sufficient.

1) A+B=7 ...means one of these is odd and one is even. So A*B has to be even.

2) If B is even, that is enough to say A*B is even.

Basically anything multiplied with an even is even.


Sent from my iPhone using GMAT Club Forum mobile app

AB COULD BE FRACTIONS , AND IF INTEGERS THEN AB , ONE OF THEM IS EVEN ( INCLUDING 0)

FROM 1

... INSUFF .. COULD BE FRACTIONS

FROM 2

B IS EVEN , STILL NO IDEA ABOUT A ( COULD BE A FRACTION)

BOTH TOGETHER

Suff ...c

really 700 lvl?

1. it can be 3.5 + 3.5 - so no. or it can be 2 and 5 - yes
2. what about A? if a =2.3 then no, if a =3 then yes
1+2 -> A and B are integers and B is even. 100% A * B even!

People often miss the fact whether variable is integer , number ,+ve ,or -ve...
i Got many question wrong because of this, but now first thing i check is whether variable is mentioned number , integer etc then i attack question...in serious GMAT time crunch situation this question will be 700+ level....

nice question stonecold

this is definitely one of them which would stump a guy in a hurry. temptations will be high to mark the answer as B. Thank you stonecold

Question looks confusing! What is being test here? I dont see the interest of this type of questions.

Why is the question stem not specifying the nature of the numbers A&B .
Hidding information on A&B just makes this kind of question confusing.

I can hear you saying that when no information is given on A&B, you have to asume that they are real numbers.
A&B can only real numbers, but also be any kind of number such as complex number.

If the aim is to test logic, then questions stem has to be more explicit.

Complex numbers are not a part of the GMAT.
If no info is given -> You cannot assume they are integers.
You have to treat them as real numbers.



The question is worded appropriately.
As it should be.



Regards
Stone Cold
_________________

Complex numbers are not considered in GMAT. When no information is given, you can only consider A & B to be real numbers.

More than quant abilities, logical reasoning is tested here. The question really tests whether you are able to identify if the given statements are sufficient enough to answer the question - yes or no.

Option C

I) Not sufficient
No information about whether A & B are integers or not.

II) Not sufficient
No information about A, whether it's an integer or not.

I) + II) Sufficient
A & B are integers, B is even. Hence, A * B is even.


Sent from my MotoG3-TE using GMAT Club Forum mobile app

"Infer - a, b can be integers, decimals or a or b can be zero.

S-1) If A, B are integers sufficient.
If A = 0 then NS.
If A or B decimals 3.3 * 3.7 = Odd * Odd = Odd. NS

S-2) B is even. No info for A. NS

S-3) Since B is even, A cannot be 0
B = 3.2 then A has to be even, though decimal. Sufficient in any case."

Answer C. Super GMAT TRap Question.

AB=Even if {A,B} are integers and at least one of the are Even;

1) A+B=7:
if A=√irrational then B=7-A=anything… answer no
if A=3 then B=7-3=4… answer yes
two answer, insufic.

2) B is even: then A = anything, answer yes/no; insufic.

(1&2) A+B=7… A+B=Odd… Odd=Even+Odd or Odd+Even… so, A and B are integers and AB=Even; sufic.

Answer (C)