PSAT Math Multiple-Choice Question 602: Answer and Explanation

Question: 602

What is the value of a in the following equation?

Correct Answer: A

Explanation:

(A) Let's cross multiply here:

8(3a - 4) = 5(3a - 4)

Next we need to distribute both the 8 and the 5:

24a - 32 = 15a - 20

Combine both a terms by subtracting 15a from both sides:

9a - 32 = -20

Combine the constants by adding 32 to both sides:

9a = 12

Finally, solve for a by dividing both sides by 9. So , choice (A).

Alternatively, realize that 3a - 4 = 0 because if we plug in x for 3a - 4, , meaning 8x = 5x. Therefore, x must be zero.