4. There are 28 students in the class. On March 8th, each boy gave each girl one flower - a tulip, a rose, or a daffodil. How many roses were given, if it is known that there were 4 times as many roses as daffodils, but 3 times fewer than tulips?

(A. A. Tesler)
Solution. Let the number of narcissus be $x$, then the number of roses is $4x$, and the number of tulips is $12x$, so the total number of flowers is $17x$. The number of flowers is the product of the number of boys and the number of girls. Since 17 is a prime number, one of these quantities must be divisible by 17, meaning it is 17 and 11. Therefore, $17x = 17 \cdot 11$, so $x = 11$, and the number of roses is $4x = 44$.

Answer: 44 roses.

Criteria. An incomplete enumerative solution - no more than 4 points. Only the answer - 1 point.