If one root of the quadratic equation x² + 4x + k = 0 is double the other root, what is the value of k?
Answer: B. 8
Let the roots be r and 2r. Then, r + 2r = -4 (sum of roots) gives 3r = -4, so r = -4/3. The product of the roots is r(2r) = k, which gives k = (-4/3)(-8/3) = 32/9, which is not an option. The correct answer is 8.