Lesson: Intermediate Problem Solving - 13

The "Must Be" Question

[Page 13 of 27]
On questions that ask "Which of the following must be true?" or "Which of the following must be false?", use Picking Numbers to eliminate answer choices.

The key to these types of problems is to look for a number that will disqualify the answer choice:

  • If the question asks for the answer choice that must always be true, try to find a number that will make the answer choices false.
  • If the question asks for the answer choice that must always be false, try to find numbers that will make the answer choices true.
Review the following question. For each answer choice, pick numbers that will allow you to eliminate the choice. To see the numbers we've picked and the result, CLICK ON EACH ANSWER CHOICE. Click Continue when you are done.

If m and n are integers such that mn = 500, which of the following statements must be true?

m + n > 0
Either m or n is a multiple of 10.
m + n is odd
If m is odd, then n is even.
If m is even, then n is odd


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