A barrel of oil is 2kg, 15 kg of oil is poured out in the first time, 15 kg is poured out in the second time, and there is still oil left in the barrel___ Kilogram

2-2 × 15-15 = 2-25-15 = 75 (kg), so the answer is: 75

There is a barrel of oil. Two fifths of the total amount is taken out in the first time. The second time, 15 kg is taken out. There are 21 kg left in the barrel. How many kg of oil is taken out in the first time

Total amount
=(15 + 21) / (2 / 1-5)
=36 × 5 / 3
=60kg

Take it out for the first time
=60 × 2 / 5
=24 kg