Hi oquiella,
This question can be solved Algebraically or by TESTing THE ANSWERS.
We're told that an author receives $0.80 for each of the FIRST 100,000 copies of her book sold and $0.60 for each additional copy (after the first 100,000). We're then told that she received $260,000 in royalties. We're asked how many copies of the book were sold.
Let's TEST THE ANSWERS.
Since Answer B is only 300,000, if she received $0.80 for each of those books (even though she'd actually receive less than that once she sold over 100,000 copies), the total revenue would be only 300,000($0.80) = $240,000. This is TOO LOW, so MORE books must have been sold.
With Answer D: 400,000...
We have $0.80(100,000) = $80,000 + $0.60(300,000) = $180,000....
$80,000 + $180,000 = $260,000
This is a MATCH for what we were told, so this MUST be the answer.
Final Answer: D
GMAT assassins aren't born, they're made,
Rich