The volume of the barrel is 540 liters. 85% of this barrel is filled with water. How many liters of water is in this barrel?

To solve this problem, we use the proportion method.
Let’s take the volume of the barrel, 540 liters, for 100%. The barrel is 85% filled with water. Let 85% of the water in the barrel be X l.
Let’s write down the correspondence.
540 l. corresponds to 100%,
X l. corresponds to 85%,
Let’s write down the proportion:
540 / X = 100/85.
To solve this proportion, we use the “cross” rule: “The product of the extreme terms of the proportion is equal to the product of the middle terms.” Let’s write down:
540 × 85 = X × 100
x = (540 × 85) / 100 = 45900/100 = 459 l.
Answer: in a barrel of 459 liters. water.