If you compound twice a year, you need to divide your annual interest rate by 2, and knowing that one thing alone lets you see that A is the right answer here.

But the math in this question is not proper math. The question tells us that Y represents some unknown value. They then write "0.0Y" in the answer choices, where we're meant to assume Y instead represents an unknown digit. It would be perfectly reasonable (correct, in fact) to assume 0.0Y means a product of 0.0 and Y. I say that interpretation is correct because if you read a question that says "k is a single digit integer between 0 and 9, and 2k > 17", then k absolutely does not represent an unknown units digit in the number '2k'. It represents an unknown value- the inequality tells us that 2 times k is greater than 17.

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