PSAT Math Multiple-Choice Question 673: Answer and Explanation

Question: 673

2m^-2 - 4m^-3 is equivalent to which of the ­following?

• A.
• B.
• C.
• D. -2m² + 4m³

Correct Answer: C

Explanation:

(C) If the negative exponent is in the numerator, it can send whatever is being raised to that exponent to the denominator, but be careful here. In both terms, only the m is being raised to the negative exponents, so the constants stay in the numerator:

However, this doesn't match an answer choice. Based on the answer choices, it looks like we may need to add the two fractions together to get just one fraction overall. To add the two fractions, we need a common denominator. If you multiplied the first fraction by , both terms would have a denominator of m³:

Now that they have a common denominator, you can add the two fractions together:

Choice (C) is correct.