Four customers came into a bakery. The first one said, “Give me half of all the donuts you have left, plus half a donut more.” The second customer said, “Give me half of all the donuts you have left, plus half a donut more.” The third customer said, “Give me three donuts.” The last customer said, “Give me half of all the donuts you have left, plus half a donut more.” This last transaction emptied the display case of donuts. How many donuts were there to start with?
