3. Answer: 5 trucks. Indeed, 5 trucks will be always enough. First four trucks can carry at least 8 tons of stones and the fifth will be able to carry all the rest. If there were 13 stones weighing $10 / 13$ tons each, then each truck would be able to carry only 3 of them, hence five cars might be needed in this case.
3. Several pounamu stones weigh altogether 10 tons and none of them weigh more than 1 tonne. A truck can carry a load which weight is at most 3 tons. What is the smallest number of trucks such that bringing all stones from the quarry will be guaranteed?