Since this question asks for the TOTAL number of animals, and the answers are numbers, this is a perfect opportunity to TEST THE ANSWERS.
We're told a few Facts about a group of animals:
1) There are D total animals
2) 12 of them are sold at a 10% profit
3) The rest are sold at a 20% loss
4) The profits and losses "cancel out"
We're asked to solve for D.
Since 12 animals were sold for a profit, while the rest were sold for a loss, the total number of animals MUST be MORE than 12. Eliminate A and B.
Since we need the profits and losses to cancel out, we're likely looking for a situation in which there were FEWER animals sold for a loss than were sold for a profit (since each individual 'loss' is so much bigger than each individual 'profit').
Let's TEST Answer C....
IF there were 18 animals, 12 were sold for a profit and 6 were sold for a loss.
IF....each animal costs $100
The 12 that were sold for a 10% profit --> $110 each ---> 12($10 profit each) = $120 profit
The 6 that were sold for a 20% loss ---> $80 each --->6($20 loss each) = $120 loss
Here, the profits and losses cancel out, so C MUST be the answer.
GMAT assassins aren't born, they're made,
Official Guide 2016 Question Breakdown:
GMAT Club Verified Reviews for EMPOWERgmat & Special Discount
EMPOWERgmat Podcast - A Wild Secret About The GMAT Algorithm