Hi AbeNeedsAnswers,
Sometimes Test Takers get confused by questions that use the phrase 'percent greater' or 'percent less', so it can be helpful to come up with simple examples to confirm that "your answer" is the correct one.
We're told that Joe grew 1 inch and that Sally grew 200% MORE than Joe did. We're asked for the number of inches that Sally grew.
IF.... Sally grew the same as Joe did, then she would have grown 1 inch
IF.... Sally grew 100% more than Joe did, then she would have grown 1+1 = 2 inches
IF.... Sally grew 200% more than Joe did, then she would have grown 1+2 = 3 inches
Final Answer: D
GMAT assassins aren't born, they're made,
Rich