The mean age of 18 students of a class is 14.5 years. Two more students of age 15 years and 16 years join the class. What is the new mean age?

By formula,

$\text{Mean} = \dfrac{\text{Total age}}{\text{No. of students}} \\[1em] \therefore 14.5 = \dfrac{\text{Total age}}{18} \\[1em] \text{Total age} = 18 \times 14.5 = 261.$

Total age of 20 students = 261 + 15 + 16 = 292 years.

So, mean age of 20 students = $\dfrac{292}{20}$ = 14.6 years.

Hence, the new mean age is 14.6 years.