Is the non-negative number r prime?

Question

(1) r = 2n, where n not equal to 1

(2) r = 2m, where m not equal to 0

kritiminocha · Answer

A.

N can be any number but 1. Hence, R can take any value but 1.

2 being a prime number and even, multiply by any number, will not give a prime number. Hence, definite answer that R is not a prime number.

Hence A.

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redskull1 · Answer

I can clearly assume n=1.5 and n= 2 and proceed .

The features of N and M have to be mentioned

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EncounterGMAT · Answer

r=prime?
(1) r = 2n, where n not equal to 1
n ≠ 1 => except 2x1, any integer (in this question, only positive numbers) cannot be a prime number. 
Answer would differ when n is a fraction. INSUFFICIENT!

(2) r = 2m, where m not equal to 0
m ≠ 0 => If m=1, r is prime but if m= any integer (in this question, only positive numbers), then r is not a prime number. Similarly, if m is fraction, answers would differ. Different answers. INSUFFICIENT!

(1) + (2) 
No difference. Will get yes/no answers. INSUFFICIENT!

Therefore, answer is option E

CrackverbalGMAT · Answer

Hi Blowice27,

Questions like these become tricky if not approached the right way. Keeping two things in mind will help boost your accuracy on DS questions:

1. Plugging In v/s Analysis : Choose your approach based on the question stem - Instead of blindly getting in to solving with the statements, use data provided (or sometimes not provided) in the question stem to determine whether you would plug in values or use analysis. When constraints are mentioned in the question, the best route is to analyze, but if constraints are given the best approach is to plug in values. For eg: If the question mentions that x is an integer and gives us 3x is even, then we can directly say that x has to be even, however if we do not have any mention of x is an integer, and 3x is even, then x can be even or a fraction.

2. Always try to prove insufficiency: Having a negative mentality while solving DS questions will help you avoid falling for traps. Always try to take examples to prove insufficiency. For a value DS question try to get multiple possibilities to prove insufficiency, for a YES/NO DS question try to get a YES and a NO to prove insufficiency.

Now coming to the question

Is the non-negative number r prime?

Since we have no constraints on 'r' being an integer, the best route here would be to plug in values.

Statement 1 : r = 2n, where n not equal to 1

If n = 0, then r = 0, this gives us a NO
If n = 3/2, then r = 3, this gives us a YES
Insufficient

Statement 2: r = 2m, where m not equal to 0

If m = 1, then r = 2, this gives us a YES
If m = 2, then r = 4, this gives us a NO

Combining the two statements

If n = 3/2 and m = 3/2, r will be 3, this gives us a YES
If n = 2 and m = 2, r will be 4, this gives us a NO

Answer is E

blowice27 · Answer

Thanks, OA has been corrected

bumpbot · Answer

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Is the non-negative number r prime?

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GMAT Data Sufficiency (DS) Questions

Is the non-negative number r prime?

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