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Is n an odd number?

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Is n an odd number?  [#permalink]

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New post 03 Sep 2018, 23:24
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

44% (01:19) correct 56% (01:11) wrong based on 61 sessions

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[Math Revolution GMAT math practice question]

Is n an odd number?

1) n is the sum of 2 prime numbers
2) n is a multiple of 11

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Re: Is n an odd number?  [#permalink]

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New post 03 Sep 2018, 23:40
MathRevolution wrote:
[Math Revolution GMAT math practice question]

Is n an odd number?

1) n is the sum of 2 prime numbers
2) n is a multiple of 11



1) n is the sum of 2 prime numbers
n=2+3=5 =odd
n=3+5=8=even
insufficient

2) n is a multiple of 11
n=22,33,44
insufficient

using both
n=22=3+19 = even
n=33=2+31=odd

insufficient
E
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Re: Is n an odd number?  [#permalink]

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New post 03 Sep 2018, 23:43
1
MathRevolution wrote:
[Math Revolution GMAT math practice question]

Is n an odd number?

1) n is the sum of 2 prime numbers
2) n is a multiple of 11


Question stem:- Is n an odd number?

St1:- n is the sum of 2 prime numbers

a) n=2+3=5, which is odd
b)n=3+5=8, which is even

Insufficient.

St2:- n is a multiple of 11
Or, n=11k, where k is a positive integer
a)when k=1, n=11, which is odd.
b) when k=2, n=22, which is even.
Insufficient.

Combined, n is the sum of 2 prime numbers and n is multiple of 11.
a) n=19+3=22 and n=11*2=22, which is even
b) n=119+2=121 and n=11*11=121, which is odd.

Insufficient.

Ans. (E)
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Re: Is n an odd number?  [#permalink]

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New post 04 Sep 2018, 17:41
MathRevolution wrote:
[Math Revolution GMAT math practice question]

Is n an odd number?

1) n is the sum of 2 prime numbers
2) n is a multiple of 11

Is n odd ?

(1+2) Insufficient:

> Take n = 22 = 3+19 to answer in the negative
> Take n = 33 = 2+31 to answer in the positive

The above follows the notations and rationale taught in the GMATH method.

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Re: Is n an odd number?  [#permalink]

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New post 06 Sep 2018, 00:32
=>
Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

Since we have 1 variable (n) and 0 equations, D is most likely to be the answer. So, we should consider each of the conditions on their own first.

Condition 1)
If \(n = 2 + 3\), then \(n = 5\) is odd and the answer is ‘yes’.
If \(n = 3 + 5\), then \(n = 8\) is even and the answer is ‘no’.
Since we don’t have a unique solution, condition 1) is not sufficient.

Condition 2)
If \(n = 11\), then n is odd and the answer is ‘yes’.
If \(n = 22\), then n is even and the answer is ‘no’.
Since we don’t have a unique solution, condition 2) is not sufficient.

Conditions 1) & 2)
If \(n = 2 + 31\), then \(n = 33\) is odd and the answer is ‘yes’.
If \(n = 13 + 31\), then \(n = 44\) is even and the answer is ‘no’
Since we don’t have a unique solution, both conditions 1) and 2) are not sufficient, when taken together.

Therefore, E is the answer.

Answer: E
If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E.
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Re: Is n an odd number?   [#permalink] 06 Sep 2018, 00:32
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