2007 AMC 8 Problems/Problem 7
Problem
The average age of people in a room is years. An -year-old person leaves the room. What is the average age of the four remaining people?
Solution
Let be the average of the remaining people.
The equation we get is
Simplify,
The answer is
OR
Since an year old left from a group of people averaging , The remaining people must total years older than . Therefore, the average is years over . Giving us .