ISEE Mathematics Achievement Question 333: Answer and Explanation

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Question: 333

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

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

(2 ? 4) × (3 ? 6) =

  • A. (9 ? 3) + 3
  • B. (6 ? 4) + 1
  • C. (5 ? 3) + 4
  • D. (8 ? 4) + 2

Correct Answer: A

Explanation:

A You will need to set the equation up based on the function defined above, and then use PEMDAS to simplify and solve for the end result. Take this question in bite-sized pieces. Start with the first set of parentheses: (2 ? 4) = (2 × 4) - (2 + 4) = (8) - (6) = 2. Next, work with the second set of parentheses: (3 ? 6) = (3 × 6) - (3 + 6) = (18) - (9) = 9. Put these values back in the original equation: (2 ? 4) × (3 ? 6) = (2) × (9) = 18. Now, test the choices to see which expression yields 18 as well. Try (A): (9 × 3) - (9 + 3) + 3 = (27) - (12) + 3 = 18. Since this matches, stop here. The correct answer is (A). Remember, if you find a question too time consuming, skip it and move on! You can come back to it later if you have time.

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