Tell you how to write! 5.2-2.7=2.5 2.5*2=5 5.2-5=0.2 The oil weighs 5 kg and the barrel weighs 0.2 kg. Analysis: The oil drum is ***5.2 kg, and the oil drum is ***2.7 kg after half use. It can be seen that the used oil weighs 5.2-2.7=2.5 (kg).