The average age of 15 students of a class is 15 years. Out of these the average age of 5 students is 14 years and that of the other 9 students is 16 years. The age of the 15th student is:

11 years

Total age of 15 students  = (15×15)years = 225years

Total age of 5 students  = (5×14)years = 70years

Total age of other 9 students  = (9×16)years = 144years

∴ Age of the 15th student  = 225−(70+144) = 225−214 = 11years.