PSAT Math Multiple-Choice Question 307: Answer and Explanation

Question: 307

In the equation , which of the following is a possible value of x - 4?

• A.
• B. 4
• C.
• D. 5

Correct Answer: A

Explanation:

A

Difficulty: Medium

Strategic Advice: When a question asks for a value of an expression, isolate that expression on one side of the equation. Do not solve for the variable because you'll have the extra step of plugging that value into the expression.

Getting to the Answer: Notice that the question asks for a possible value of x - 4, not a possible value of x. Isolate x - 4 on one side of the equation by multiplying both sides by x - 4 and taking the square root of both sides:

Thus, (A) is correct. Watch out for traps like (C), which is a possible value of x.

An alternative strategy is to backsolve, plugging each choice in for x - 4 to see which results in a true statement.