Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Re: If x and y are two different prime numbers, which of the [#permalink]
08 Jun 2012, 08:29
If x and y are two different prime numbers, which of the following cannot be true?
A. xy is odd. B. x + y is even. C. x + y is odd. D. xy is even. E. x/y is an integer
A prime number is a positive integer with exactly two distinct positive divisors: 1 and itself. So, a prime number cannot be a multiple of another prime number. Which makes option E not possible (x/y=integer means that x is a multiple of y).
All other options are possible: A. xy is odd --> x=3 and y=5; B. x + y is even --> x=3 and y=5; C. x + y is odd --> x=2 and y=3; D. xy is even --> x=2 and y=3;
Re: If x and y are two distinct prime numbers, which of the following cann [#permalink]
09 Sep 2014, 18:28
The best way to attack this question is to Plug-In simple prime numbers to prove the answer choices. Don't forget that 2 is the first prime number, and also the only even one. As a refresher, the definition of a prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.
(A) x*y is odd. Let's choose x=3, y=5, so x*y = 15.
(B) x*y is even. Let's choose x=2, y=3, so x*y = 10.
(C) x-y is odd. Let's choose x=3, y=2, so x-y = 1.
(D) x-y is even. Let's choose x=5, y=3, so x-y = 2.
Thus, E is the only answer choice left, and must be the answer.