(4) Total age of initial 30 students = 14 years 4 months × 30 = 430 years Total age of 35 students = 13 years 9 months × 35 = (455 + 26) years 3 months = 481 years 3 months ∴Total age of 4 new students= 481 years 3 months – 430 years – 9 years 11 months = 481 years 3 months – 439 years 11 months = 41 years 4 months ∴Required average =