1. 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 10 times fewer than tulips? (A. A. Tesler)
Solution. This is a more complex version of problem 4 for 5th grade.

Let the number of narcissus be $x$, then the number of roses is $4x$, and the number of tulips is $40x$, so the total number of flowers is $45x$. The number of flowers is the product of the number of boys and the number of girls. If there are $m$ boys, then $m(28-m)$ is divisible by 45. Both factors cannot be divisible by 3, so one of them is divisible by 9, and the other by 5. The only option is $-18 \cdot 10$. Therefore, $45x = 180$, which means $x = 4$, and the required number of roses is $4x = 16$.

Answer: 16 roses.

Criteria. An incomplete enumerative solution - no more than 4 points.