The given question is a challenging GMAT data sufficiency question in Inequalities. Concepts covered: Inequalities, absolute values and number properties
This data sufficiency problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. You have to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements, plus your knowledge of mathematics and everyday facts (such as the number of days in a leap year or the meaning of the word counterclockwise), you must indicate whether -
All numbers used are real numbers.
A figure accompanying a data sufficiency question will conform to the information given in the question but will not necessarily conform to the additional information given in statements (1) and (2)
Lines shown as straight can be assumed to be straight and lines that appear jagged can also be assumed to be straight
You may assume that the positions of points, angles, regions, etc. exist in the order shown and that angle measures are greater than zero.
All figures lie in a plane unless otherwise indicated.
In data sufficiency problems that ask for the value of a quantity, the data given in the statement are sufficient only when it is possible to determine exactly one numerical value for the quantity.
Question 26: Is x|x| = x2?
Statement 1: x(1 – x2) < 0
Statement 2: x(1 – x) < 0
Q1. When is the data sufficient?
If we are able to get a conclusive YES or NO, the data is sufficient.
Q2. What should you watch out for ?
If x > 0, x |x| = x2
If x = 0, x |x| = x2
If x < 0, x |x| is negative and x2 is positive. So, x |x| < x2 ?
So, the question is essentially asking whether x is non negative i.e., Is x ≥ 0 ?
Statement 1: x(1 – x2) < 0
i.e., x - x3 < 0 or x < x3
For what values of x will x < x3 ?
Interval 1: (1 < x < ∞)
x < x3. Here, x is greater than zero. Answer to the question - YES
Interval 2: (-1 < x < 0)
x < x3. Here, x is lesser than zero. Answer to the question - NO
We are not able to get a conclusive answer using Statement 1.
Hence, statement 1 is not sufficient.
Eliminate answer option A and D.
Statement 2: x(1 - x) < 0
i.e., x – x2 < 0 or x < x2
For what values of x will x < x2 ?
Interval 1: (1 < x < ∞)
x < x2. Here, x is greater than zero. Answer to the question - YES
Interval 2: (-1 < x < 0)
x < x2. Here, x is lesser than zero. Answer to the question - NO
We are not able to get a conclusive answer using Statement 2.
Hence, statement 2 is not sufficient.
Eliminate answer option B.
Statements: From Statement 1: x < x3
From Statement 2: x < x2
Both conditions hold good in the following intervals,
Interval 1: (1 < x < ∞)
x < x3 and x < x2. Here, x is greater than zero. Answer to the question - YES
Interval 2: (-∞ < x < 0)
x < x3 and x < x2. Here, x is lesser than zero. Answer to the question - NO
Despite combining the statements, we are not able to get a conclusive answer.
Eliminate answer option C.
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