454. Several identical boxes together weigh 10 tons, with each of them weighing no more than 1 ton. What is the minimum number of three-ton trucks needed to haul away all this cargo in one trip?
$\triangle$ Four trucks may not be enough. For example, if there are 13 identical boxes weighing $\frac{10}{13}$ tons each, then in one of the trucks, you cannot place more than three boxes, because with four boxes, the weight is $4 \cdot \frac{10}{13}$ tons, which is more than 3 tons. In this case, with four trucks, you can transport no more than 12 boxes out of 13.

Five trucks are sufficient in all cases. Indeed, we can load at least 2 tons of cargo into each truck: if less than 2 tons are loaded, then you can add another box (or boxes) since each box weighs no more than one ton by the condition. Therefore, with five trucks, you can load at least 10 tons of cargo.

Answer: 5.