ISEE Mathematics Achievement Question 44: Answer and Explanation

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Test Information

Question: 44

2. Solve for x: 2x2 + 3 = 21.

  • A. ± 3
  • B. ± 5
  • C. ± 9
  • D. ± 10

Correct Answer: A

Explanation:

The correct answer is (A).

2x2 + 3 = 21

2x2 = 21 - 3

2x2 = 18

x2 = 9

x = ± 3

You should have been able to predict that x would be a small number, since, according to the equation, twice its square is no larger than 21.

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