1. At a melon stand, watermelons and melons are sold. The average weight of a watermelon is 12 kg, and the average weight of a melon is 6 kg. How many watermelons and how many melons are there at the stand, if their total number is 300, and the total weight is 2.4 tons?
Answer: watermelons - 100, melons - 200.

Let $x$ and $y$ represent the number of watermelons and melons, respectively, then we get $12x + 6y = 2400$ and $x + y = 300$, from which $x = 100$ and $y = 200$.