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Updated on: 08 May 2015, 08:29
Originally posted by bjshukla on 02 Jan 2011, 14:08.
Last edited by Bunuel on 08 May 2015, 08:29, edited 1 time in total.
Last edited by Bunuel on 08 May 2015, 08:29, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
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Question Stats:
59% (01:23) correct
41%
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If x and y are prime numbers, is y(x-3) odd?
(1) x > 10
(2) y < 3
(1) x > 10
(2) y < 3
Hello,
Book: Kaplan GMAT Premier 2011
Pages: 457 and 458
For the data sufficiency problem "If x and y are prime numbers, is y(x-3) odd?" on page 457, explained answer on page 458 is D (Each statement alone is sufficient.)
2 statements are:
1. x > 10
2. y < 3
However, I feel that answer should be A (only 1 is sufficient).
Statement 2 is not sufficient, because:
1. If we pick y = 2 and x = 2, equation yields 2(-1) = -2 => Even number
2. If we pick y = 1 and x = 2, equation yields 1(-1) = -1 => Odd number
Thus depending on what we pick, the result can be even or odd...hence we cannot conclusively say if y(x-3) will be odd or not based on statement 2.
May you please advise if I am not approaching this correctly?
Thank you for your help in advance!
Book: Kaplan GMAT Premier 2011
Pages: 457 and 458
For the data sufficiency problem "If x and y are prime numbers, is y(x-3) odd?" on page 457, explained answer on page 458 is D (Each statement alone is sufficient.)
2 statements are:
1. x > 10
2. y < 3
However, I feel that answer should be A (only 1 is sufficient).
Statement 2 is not sufficient, because:
1. If we pick y = 2 and x = 2, equation yields 2(-1) = -2 => Even number
2. If we pick y = 1 and x = 2, equation yields 1(-1) = -1 => Odd number
Thus depending on what we pick, the result can be even or odd...hence we cannot conclusively say if y(x-3) will be odd or not based on statement 2.
May you please advise if I am not approaching this correctly?
Thank you for your help in advance!
02 Jan 2011, 14:32
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bjshukla
If x and y are prime numbers, is y(x-3) odd?
Note that we are told that both x and y are prime numbers, also note that 1 is not a prime number.
Now, in order the product of 2 integers to be odd both must be odd, so y(x-3) to be odd y must be any odd prime and x must be the only even prime 2, so that x-3=even-odd=odd. In all other cases given product will be even.
(1) x > 10 --> x is not 2, so the product is even. Sufficient.
Or: x is a prime number more than 10, so it's odd --> x-3=odd-odd=even --> y(x-3)=y*even=even.
(2) y < 3 --> the only prime less than 3 is 2, so y(x-3)=even*(x-3)=even. Sufficient.
Answer: D.
For more check Number Theory chapter of Math Book: math-number-theory-88376.html
Hope it helps.
03 Nov 2011, 08:42
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1. Only even prime is 2, so if x>10 then (x-3) is even. SUFFICIENT.
2. y<3 does not prove anything. NOT SUFFICIENT.
Hence ans is A
2. y<3 does not prove anything. NOT SUFFICIENT.
Hence ans is A
