3. Kolya says that two chocolate bars are more expensive than five gums, Sasha - that three chocolate bars are more expensive than eight gums. When this was checked, only one of them was right. Is it true that 7 chocolate bars are more expensive than 19 gums? Don't forget to justify your answer.
Solution. Let the price of a chocolate bar be $c$, and the price of a gum be $g$. Kolya says that $2 c>5 g$ or $6 c>15 g$, while Sasha says that $3 c>8 g$ or $6 c>16 g$. If Sasha were right, then Kolya would also be right, which contradicts the condition. Therefore, Kolya is right, but not Sasha, and in fact $3 c \leqslant 8 g$ or $21 c \leqslant 56 g<57 g$, that is, $21 c<57 g$ and $7 c<19 g$. Answer: false.

Criterion. Only the answer - 0 points. Only specific cases with concrete prices of the chocolate bar and gum - 1 point. If the proof uses relations of the type "ح" (approximately equal) - no more than 3 points.