From the cream, 18 kg of butter were obtained, which is one-fifth of the mass of cream, how much cream was collected.

1. We know that 18 kg of butter was obtained from a certain amount of cream.

2. Let’s calculate how much cream was taken in order to get a given amount, if we know from the condition of the problem that the resulting butter is one-fifth, that is, 1/5 of the amount of cream taken. This means that we need the mass of butter that has been prepared to be divided into the part that this butter is relative to the cream taken. Let’s write down the solution:

18 / 1/5 = 18 * 5/1 = 90 kg.

Answer: 90 kg of cream was taken to prepare the butter.