A shopkeeper bought a total of 20 bags of grains having an average weight of 60.5 kg per bag. Out of these, the average weight of the 7 rice bags was 60 kg per bag, while the average weight of a wheat bag was 4 kg more than that of a maize bag. If 9 of the bags contained wheat while the remaining contained maize, what is the average weight of a maize bag?

Total weight of 20 bags = 20 × 60.5 = 1210 kg. Weight of 7 rice bags = 7 × 60 = 420 kg. Remaining 13 bags are wheat and maize. 9 wheat bags, so 4 maize bags. Let maize bag weight = m kg. Then wheat bag weight = m + 4 kg. Total: 420 + 9(m + 4) + 4m = 1210. Solving: 420 + 9m + 36 + 4m = 1210, so 13m + 456 = 1210, 13m = 754, m = 58 kg. Average weight of maize bag = 58 kg.