ISEE Mathematics Achievement Question 44: Answer and Explanation
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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.