The mean age of 5 people in a room is 31 years. A person enters the room.
The mean age is now 30.
What is the age of the person who entered the room?​

25 year

Step-by-step explanation:

Mean = sum/no. *of observations

Initially, number of people = 5 & let the sum of their ages be S.

=> 31 = S/5

=> 155 = S

When one more entered, number = 6. Let his age be 'a'.

Sum of ages = S + a = 155 + a

=> 30 = (155 + a)/6

=> 180 = 155 + a

=> 25 = a