A barrel of oil, the first time to use more than half of its 5 kg, the second time to use the remaining half less than 3 kg, the third time to use 12 kg, there are 8 kg. How many kg of this barrel of oil?

A barrel of oil, the first time to use more than half of its 5 kg, the second time to use the remaining half less than 3 kg, the third time to use 12 kg, there are 8 kg. How many kg of this barrel of oil?

(12 + 8-3) × 2, = (20-3) × 2, = 17 × 2, = 34 (kg); (34 + 5) × 2, = 39 × 2, = 78 (kg); a: this barrel of oil used to be 78 kg

For a barrel of oil, after the first 12 kg, 15 kg was poured in, and after the second 20 kg, 18 kg was left. How many kg was this barrel of oil?

Backward method
18 + 20 = 38 (kg)
38-15 = 23 (kg)
23 + 12 = 35 (kg)
So it turned out to be 35 kg

When a bucket of oil is poured out 2 / 5 kg for the first time and 1 / 3 of the whole bucket for the second time, there is still 12 / 5 kg left in the bucket. How many kg is there in this bucket?

Oily
1－1/3＝2/3
yes
2 / 5 + 12 / 5 = 14 / 5kg
How much is this barrel of oil
14 / 5 △ 2 / 3 = 21 / 5kg

A little confused. A barrel of oil is used up in two times. Two thirds of the oil is used in the first time and two-thirds of the kilogram is used in the second time. How many kilogram is the barrel of oil?
Can you be more specific

2 / 3 ÷ (1-2 / 3) = 2kg
There are two kilos of oil in this barrel