Discussion
If x and y are prime numbers, then which one of the following cannot equal x − y?
*This question is included in Nova Math - Problem Set A: Substitution, question #10
(A) | 1 |
(B) | ... |
(C) | ... |
(D) | ... |
(E) | ... |
(F) | ... |
The solution is
Posted: 07/24/2012 18:45
What is the definition of a prime number?
Posted: 07/24/2012 19:27
Katie, a prime number is an integer that can only be wholly divided by 1 and itself.
Posted: 10/02/2012 23:52
In method 2, why is x set equal to 2k+1 and y set equal to 2h+1?
Posted: 10/03/2012 00:08
Kayla, that makes them always odd, since prime numbers are always odd, except for 2.
Posted: 07/26/2013 21:21
Why for some substitution questions, you maintain the same numbers you're substituting to test each answer, but for other questions, like this one, you change the numbers you substitute? In other words, how can you say that you'd never end up with x-y = 13, unless you tested tons of prime numbers?
Posted: 07/27/2013 12:20
David, in this particular question, since we have to test for x-y and we are told x and y are prime, we only need to test only for prime numbers that are just larger than the answer. Since every choice is different then we have to try different prime numbers. Luckily for us there are not that many prime numbers in the vicinity of the answer choices.