The mean age of 5 people in a room is 39 years. A person enters the room. The mean age is now 40. What is the age of the person who entered the room?

Suppose you are analyzing the relationship between time and distance given in a table,and there are 4 values for each quantity.you divide distance 2 minus distance 1 by time 2 minus time 1.you then divide distance 4 minus distance 3 by time 4 minus time 3 and get a different answer.what can you say about the relationship?