10. Transportation of cargo. Several boxes together weigh 10 tons, with each of them weighing no more than one ton. What is the minimum number of three-ton trucks needed to haul this cargo?
10. Let's show that a) four three-ton trucks may not be enough, b) five three-ton trucks will always be enough. Note that at any moment during loading, there is a truck with less than 2 tons of cargo (otherwise, the total weight of the cargo would be more than 10 tons). Therefore, we will load the trucks with boxes in turn until they are "full," that is, as long as it is possible.