For the quadratic equation x^2 - 4x + k = 0 to have real roots, what is the minimum value of k?
Answer: B. 4
The discriminant must be non-negative for real roots. The discriminant is b^2 - 4ac = (-4)^2 - 4(1)(k) = 16 - 4k. Setting this greater than or equal to 0 gives k ? 4.