Answer:
27 years old
Explanation:
There are originally 5 people in the room.
Their ages are: 16, 25, 23, 12, 17
The sum of their ages is: 93
One person enters the room. That person's age is unknown, so we call it x.
The sum of the ages of the 6 people is:
x + 93
There are 6 people in the room now, so the mean age is (total age divided by number of people):
(x + 93)/6
We are told the mean age is 20.
(x + 93)/6 = 20
x + 93 = 120
x = 27
Answer: 27 years old