In this problem, it tries to trick you by making you focus on whats wrong with the 5th person, however it details a 13th person, which is the largest number present in this problem.
That being said, by assumption, there are at least 13 people in said circle.
A way you can show work is just not use the commas then subtract then put the commas in when you're done. And, if the bigger number isn't as big or has as many numbers behind the decimal as the first one, add a zero at the end.
