The mean age of 5 people in a room is 40 years.

A person enters the room.

The mean age is now 35.

What is the age of the person who entered the room?

the answer is 40

the person entering the room is 10 years old

Step-by-step explanation:

x / 5 = 40

x = 40 * 5

x = 200

so the total of all the ages of 5 people is 200

x / 6 = 35

x = 35 * 6

x = 210

the total of all the ages of 6 people would have to be 210 for there to be a mean age of 35

therefore, a ten year old kid entering the room, will make up the difference