Answer:
57 years
Explanation:
The mean of a set of numbers is given as the ratio of the sum of the numbers to the number of numbers in the given data set.
Hence given that the age of 5 people are 17, 21, 15, 15, 25 and a 6th person joins the set, making the mean age 25, let the age of the new person that joined be x then
25 = (x + 17 + 21 + 15 + 15 + 25)/6
25 = (x + 93)/6
Multiply both sides by 6
150 = x + 93
subtract 93 from both sides
x = 150 - 93
x = 57 years
The age of the person who entered the room is 57 years