The average weight of a class of 40 students is 30 kg and the average weight of a class of 20 students is 15 kg. Find the average weight of both the classes combined.

25 kg

Total Weight = No. of students × Average

Class₁ = 40 × 30 = 1200kg

Class₂ = 20 × 15 = 300 kg

Average of both classes = \(\frac{Total\;weight}{Total\;no.}\) 

⇒ \(\frac{1500}{60}\) = 25 kg