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You are here: Home / Quant Questions / Arithmetic / Data Sufficiency : Number Properties and Probability

Data Sufficiency : Number Properties and Probability

March 17, 2014 By K S Baskar 1 Comment

GMAT DS Probability

A GMAT 700 level Data Sufficiency Question | Number properties and Probability

Question
Set A contains distinct integers: A = {2,4,6,-8,x,y}. When two numbers from this set are picked and multiplied, what is the probability that the product is less than zero?
(1) x*y is not equal to zero.
(2) |x| = |y|

 

 
Correct Answer is choice B. Statement 2 alone is sufficient. 
 

Video Explanation

Explanatory Answer

Alternatively, here is the text based explanation for the question.

The product of two numbers picked will be less than zero if one of the numbers is positive and the other is negative.

Statement 1 clearly indicates that neither x nor y is 0.

However, that alone is not sufficient because the probability of the product being less than 0 is dependent on how many of the 6 numbers is negative.

So, statement 1 is NOT sufficient.

Statement 2 points to the fact that the magnitude of x an y are same. 

Both could be positive, both negative, one negative and the other positive or both zeroes.

However, the possibility of both being simultaneously positive or negative or zero can be eliminated as the question stem states that these are distinct integers. So, one of x or y has to be positive and the other negative.

So, we know that there are 4 positive numbers and 2 negative numbers. 

Hence, we can determine the probability.

Note: We are interested only in knowing whether we will get a unique answer. Do not lose 20 to 30 seconds trying to compute the probability.

So, statement 2 is alone is sufficient.

Hence, choice B is the answer.

Additional GMAT Data Sufficiency Questions @ https://practice-questions.wizako.com/gmat/quant/data-sufficiency/

 

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Filed Under: Arithmetic Tagged With: GMAT Data Sufficiency, GMAT DS, GMAT Number Properties, GMAT Number Theory, GMAT Probability

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Comments

  1. dailydramaqueen says

    June 1, 2016 at 6:17 pm

    hi, I am not sure I get the explanation. surely x and y could both be positive or negative while being distinct?
    For example x=3 and y=4?

    Reply

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