Troy is writing a book of short stories. It is his
goal to write one short story this month, two
short stories next month, three short stories
the following month, and so on for 13 more
months. How many stories will he have written
at the end of sixteen months?
You just add 1 + 2 + 3 + 4 + 5 + 6... all the way to 13, and then at the end of 16 months, Troy still only wrote 91 stories since he only wrote them up until 13 months, and then stopped afterwards.