SSAT Math Question 221: Answer and Explanation
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Question: 221
5. If (xa)3 = x15 and = x7, then b -a =
- A. –4
- B. –2
- C. 2
- D. 4
Correct Answer: D
Explanation:
The answer is D
Solve for the variables by applying the rules of exponents. When an exponential expression is raised to another power, multiply the exponents. Therefore, (xa)3 = x3a = x15. Therefore, 3a = 15, and a = 5. When exponential expressions with like bases are divided, subtract the exponents. Therefore, = xb-2 = x7. Therefore, b - 2 = 7, and b = 9. 9 - 5 = 4.