To find the mean age of the group of people, we need to calculate the sum of the product of each age range and the corresponding number of people, and divide by the total number of people in the group.
So, using the assume mean of 13 years, we can assume that the midpoint of the age range 1-5 is 3 years, the midpoint of 6-10 is 8 years, and so on. Then, we can calculate the sum of the products:
(3 x 18) + (8 x 12) + (13 x 25) + (18 x 15) + (23 x 20) + (28 x 10) = 1299
Next, we need to divide by the total number of people in the group:
18 + 12 + 25 + 15 + 20 + 10 = 100
So the mean age of the group is:
1299 / 100 = 12.99 years (rounded to two decimal places)
Therefore, the mean age of the group of people is approximately 12.99 years.