6. A family of beekeepers brought containers of honey to the fair with volumes of $13,15,16,17,19,21$ liters. In August, three containers were sold in full, and in September, two more, and it turned out that in August they sold twice as much honey as in September. Determine which containers were emptied in August. In your answer, indicate the largest volume. #
# Solution:

A total of $13+15+16+17+19+21=101$ liters of honey were brought. The amount of honey sold is divisible by three. Therefore, the volume of the unsold container must give a remainder of 2 when divided by 3 (the same as 101), i.e., 17 liters. Thus, 101-17=84 liters were sold, with one-third of 84 liters, or 28 liters, sold in September. This corresponds to the 13 and 15-liter containers. In August, the containers of 16, 19, and 21 liters were sold. The largest of these is 21 liters.

Answer: 21.