One minute's work $= (1/20) + (1/30) = (3+2)/60 = 5/60 = 1/12$. Time taken $= 12$ minutes.
एक मिनट का कार्य $= (1/20) + (1/30) = (3+2)/60 = 5/60 = 1/12$। लगा समय $= 12$ मिनट।