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

40

Step-by-step explanation:

5 people in the room have 5*40 = 200 years altogether

a new person is X years old.

Now 6 people have (200 + x) years altogether.

Mean age of 6 people is (200+x) / 6. and it is also = 40.

So,

(200+x) / 6 = 40

200 + x = 240

x = 40