6.2. On the plate, there were 15 doughnuts. Karlson took three times more doughnuts than Little Man, and Little Man's dog Bibbo took three times fewer than Little Man. How many doughnuts are left on the plate? Explain your answer.
Answer: 2 doughnuts are left.

From the condition of the problem, it follows that Little One took three times as many doughnuts as Bimbo, and Karlson took three times as many doughnuts as Little One. We can reason in different ways from here.

First method. If Bimbo took one doughnut, then Little One took three doughnuts, and Karlson took nine doughnuts, so together they took $1+3+9=13$ doughnuts. Thus, two doughnuts are left on the plate.

If Bimbo had taken two doughnuts or more, then Little One would have taken six doughnuts or more, and Karlson would have taken 18 doughnuts or more, which is impossible.

Second method. Let Bimbo take $x$ doughnuts, then Little One took $3x$ doughnuts, and Karlson took $3 \cdot 3x = 9x$ doughnuts. Then together they took $x + 3x + 9x = 13x$ doughnuts. Since the number $13x$ must not exceed 15, the only possible natural value for $x$ is 1. Therefore, together they ate 13 doughnuts, and two doughnuts are left on the plate.

+ a complete and justified solution

$\pm$ the correct answer is provided, it is shown that it satisfies the condition, and there is a statement that it is the only one

$\pm$ the number of doughnuts each person ate is justified, but the explicit answer to the question is not provided

干 the correct answer is provided, it is shown that it satisfies the condition, but there is no mention of its uniqueness

干 only the correct answer is provided