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AlgebraHardParameter values that give a positive solution

Algebra practice question

For which values of the constant k does the equation 3x + k = 5 have a positive solution for x?

  1. A. k < 5Correct
  2. B. k > 5
  3. C. k < −5
  4. D. k > −5

Answer: A. k < 5

x = (5 − k)/3, which is positive exactly when 5 − k > 0, that is, k < 5.

Why the other answers are wrong

B. k > 5
For k > 5 the solution is negative.
C. k < −5
k < −5 is only part of the answer; values like k = 0 also work.
D. k > −5
k > −5 includes k = 10, which gives x = −5/3.

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