2.
Explanation
Mean = (Total Sum of Ages) / (Total Number of Students)
the sum of ages for each group:
For the first group of 50 students with a mean age of 15 years:
Sum of Ages in Group 1 = 50 students * 15 years/student = 750 years
For the second group of 70 students with a mean age of 20 years:
Sum of Ages in Group 2 = 70 students * 20 years/student = 1400 years
the total sum of ages for all 120 students together:
Total Sum of Ages = Sum of Ages in Group 1 + Sum of Ages in Group 2
Total Sum of Ages = 750 years + 1400 years = 2150 years
the mean age of all 120 students together:
Mean = Total Sum of Ages / Total Number of Students
Mean = 2150 years / 120 students ≈ 17.92 years
So, the mean age of all 120 students together is approximately 17.92 years.