ISEE Mathematics Achievement Question 332: Answer and Explanation

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Question: 332

4. For all real numbers d and y, d ? y = (d × y) - (d + y).

[Example: 3 ? 2 = (3 × 2) - (3 + 2) = 6 - 5 = 1]

If K (4 ? 3) = 30, then K =

  • A. 3
  • B. 4
  • C. 5
  • D. 6

Correct Answer: D

Explanation:

D This question asks to first find the result of the function, and then to find the unknown K. Take this question in bite-sized pieces. Start with the parentheses first. Solve for 4 ? 3: (4 × 3) - (4 + 3) = (12) - (7) = 5. Next, plug 5 into the equation to find K: K(5) = 30. Divide by 5 on both sides to find that K equals 6. The correct answer is (D).

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