There are empty, half-empty and full containers of wine. It is necessary to distribute them fairly to the girls, without pouring anything anywhere.

Three friends want to share 21 barrels among themselves, of which seven are full of wine to the brim, seven are half full and seven are empty. How to do this without pouring liquid so that each girl has an equal amount of wine and containers? The capacity of all kegs is the same. And yes: her friends also need empty containers, so the good will not be lost.

The girls have 21 barrels in total. This means that each friend should get 21 ÷ 3 = 7 containers. If wine could be poured, then seven full and seven half-full barrels would make 7 + 7 × 0.5 = 7 + 3.5 = 10.5 kegs of wine. This means that each friend should get 10.5 ÷ 3 = 3.5 kegs of wine.

Let's compose this amount of liquid from seven full and seven half-full containers that are available:

- the first friend will receive three full barrels and one half full;

- the second will also have three full containers and one half full;

- the third will get one last full barrel and the remaining five half full, in total 5 × 0.5 = 2.5 kegs of wine.

Now let's determine how many empty containers each friend will have. The first and second already have four barrels of wine. To the required seven pieces, they need to add three empty ones. The remaining barrel without wine must be given to a third friend, who already has six containers.

Here's what happens: the first and second girls will have three full, one half full and three empty barrels, the third - one full, five half full and one empty.