11.1. A unified control test in mathematics was conducted among all eleventh-graders in the school. As a result, 5/8 of the students received fives, 11/20 of the number of excellent students received fours, and the remaining three eleventh-graders did not come to the test due to illness. How many eleventh-graders are there in the school
Answer: 96.

The share of students who received fours is 55/160. The share of students who received fives and fours is $5 / 8 + 55 / 160 = 155 / 160$. Thus, the share of students who missed the exam is $5 / 160 = 1 / 32$. Let $N-$ be the number of eleventh graders, then from the condition $N / 32 = 3$ and $N = 96$.