Math problem: a barrel of oil weighs 310 kg, half of which is 160 kg. How many kg does the oil and barrel weigh?

linear equation in two unknowns
If the oil weight is x kg and the barrel weight is y kg, the following results are obtained:
X + y = 310 and X / 2 + y = 160
Y = 310-x, substituting into formula 2
X / 2 + 310-x = 160
X = 300 kg
Then y = 10 kg

A barrel of oil weighs 20 kg. After 3 / 5 of it is used, if the barrel weighs 5 kg, how many kg does it weigh?

Use 20 × (1-3 / 5) to get 8 (kg), calculate 3 / 5 weight of oil, and then 8-5 = 3 (kg)

A barrel of oil weighs 65 kg. After half of the oil is used, a barrel of oil weighs 35 kg. Do you know how much a barrel weighs?

65-(65-35)*2
=65-60
=5
A: the barrel weighs 5kg

A barrel of oil weighs 80 kg. After 4% is used, there are 38 kg left. How much is the weight of oil?
It's 30 kilos left

If there is XKG oil in the barrel, the mass of the barrel is 80-xkg,
∵ after using 4% of the oil, the weight of the barrel is 30kg
The first-order equation of one variable with respect to X can be listed
(4％x)+(80-x)=30,
(4％+1)x=80-30,
1.04x=50,
The solution is x ≈ 48
So the oil weighs 48 kg

Math problem: a barrel of oil weighs 310 kg, half of which is 160 kg. How many kg does the oil and barrel weigh?