If the average age of three classes A, B and C having number of students 30, 45 and 60 is 24, 28 and 21 respectively, then find the average age of all three classes.

24

Class A total age = 30 × 24 ⇒ 720

Class B total age = 45 × 28 ⇒ 1260

Class C total age = 60 × 21 ⇒ 1260

Total age of A, B and C =        3240

Total average ⇒ \(\frac{total\;age}{total\;no,}\) = \(\frac{3240}{135}\) ⇒  24