Question: Bernie has a collection of 18 unique postcards. He decided to sell half his collection for $15 per postcard. After he has successfully sold his postcards he decided to spend all the earned money to buy new postcards for $5 each. How many postcards does Bernie have after all his transactions? Think carefully first, then make a decision:
Half of Bernie's collection means 18 * 0.5 = 9 postcards. So he was able to sell 9 postcards for 9 * 15 = $135. He decided to spend all of his money on new postcards for $5 each, so he was able to buy 135 / 5 = 27 new postcards. This means Bernie has 9 + 27 = 36 postcards after all. So the answer is 36.