PSAT Math Multiple-Choice Question 7: Answer and Explanation

Question: 7

Which of the following expressions is equivalent to ?

• A.
• B. 3b³c
• C.
• D. 20.25b³c

Correct Answer: A

Explanation:

A

The question asks for an equivalent form of an expression. Notice the fractional exponents in the answer choices; when dealing with a question about fractional exponents, remember the exponent rules. Start with applying the root to the coefficient 81. Use your calculator to find = 3. Eliminate (C) and (D) because these answer choices include the wrong coefficient. Next, apply the root to the b³ term. In a fractional exponent, the numerator is the power the base is raised to and the denominator is the root of the base. Therefore, . Eliminate (B) because this answer choice includes b³ instead. Similarly, , and (B) can be eliminated because it includes c instead. The correct answer is (A).