Is 13N a positive number?

Question

(1) -21N is a negative number
(2) N^2 < 1

Kurtosis · Answer

St1: -ve * +ve = -ve. So N is positive. Sufficient

St2: -1 < N < 1. N can be positive or negative. Not sufficient

Answer: A

Mo2men · Answer

1) -21 N = -ve .. so N is clear +.......Suff

2) (1/2) ^2 & (-1/2)^2 is less than one So N could either -ve or +ve.........Insuff

Answer: A

MathRevolution · Answer

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution. Is 13N a positive number? (1) -21N is a negative number (2) N^2 < 1 When you modify the original condition and the question, 13n>0? becomes n>0?. There are 1 variables(n), which should match with the number of equations. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer. For 1), divide -21n<0 with -21 and n>0 is yes, which is sufficient. For 2), from -1

BrentGMATPrepNow · Answer

Target question :    Is 13N a positive number?

Statement 1 : -21N is a negative number   
We know that (NEGATIVE)(POSITIVE) = NEGATIVE
Since -21 is NEGATIVE, it must be the case that N is POSITIVE
If N is POSITIVE, then  13N is definitely a positive number 
Since we can answer the  target question  with certainty, statement 1 is SUFFICIENT

Statement 2 : N² < 1  
There are several values of N that satisfy statement 2. Here are two: 
Case a: N = 1/2, in which case N² = (1/2)² = 1/4, which is less than 1. In this case  13N = (13)(1/2) = 6.5. So, 13N is POSITIVE 
Case b: N = -1/2, in which case N² = (-1/2)² = 1/4, which is less than 1. In this case  13N = (13)(-1/2) = -6.5. So, 13N is NEGATIVE 
Since we cannot answer the  target question  with certainty, statement 2 is NOT SUFFICIENT

Answer:  A

Cheers,
Brent

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Is 13N a positive number?

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Is 13N a positive number?

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