Question

The mean age of 5 people in a room is 39 years.

A person enters the room.
The mean age is now 36.
What is the age of the person who entered the room?​

Answer 1

The age of the person who entered the room is 21.

Explanation:

Mean of 5 peoples = 39

i.e.

Sum / 5 = 39

Sum = 39 x 5

Sum = 195

Mean after one person enters the room = 36

Let x be the age of the new person.

Then

Mean = (Sum + x)/ 6

36 = (195 + x)/6

36 x 6 = 195 + x

216 = 195 + x

x = 216 - 195

x = 21

Answer 2

fast multiply 5 by 39 to get the total age of the five people now as you are told those per 5 so imagine the six person being you if you enter you're going to add to their ages so they mean is going to be for six people so take the six people x their mean age now we have two different total ages for the five people and for the six people subtract the total age of the 5 from the 6th total ages to get the age of the person who entered the room if you don't understand please ask me and be willing to help