Get detailed explanations to advanced GMAT questions.

If k is negative, which of the following must also be negative?

Option A:

(-k)^2

Option B:

(-1)k

Option C:

1-k

Option D:

k+1

Option E:

k-1

Option E is the correct answer.

For MUST-BE questions, Plugging- In

Given k is negative, so let’s take k = -1.

Substitute in the answer choices.

A. (-k)^2 –> (-(-1))^2 = 1 – Positive – So eliminate.

B. (-1)k –> (-1)k = (-1)(-1) = 1 – Positive – So eliminate.

C. 1-k –> 1-k = 1-(-1) -2– Positive – So eliminate.

D. k+1 –> k+1 = -1+1 = 0 –Neither Positive or Negative – So eliminate.

E. k-1 –> k-1 = -1-1 = -2—Negative-So this is the answer.

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