## Task 1 - 100931

Günter spent a number of days in a camp with his FDJ group during his vacation. Every day, exactly two students from his group were assigned to table duty in the morning and exactly two students in the afternoon. Over the days, all students in his group were assigned to this table duty equally often.

Furthermore, the following is known:

(1) Günter was assigned to table duty on exactly 6 days.

(2) If he had table duty in the afternoon, he did not have it in the morning.

(3) He did not have table duty in the afternoon on exactly 13 of these days.

(4) He did not have table duty in the morning on exactly 11 of these days.

How many students were in Günter's group?
According to (3) and (4), he had exactly twice as many morning shifts as afternoon shifts, and since he never had both morning and afternoon shifts on the same day according to (2), he was assigned to morning shifts on exactly four days, afternoon shifts on two days, and was not busy on 13-4=11-2=9 days.

Thus, the camp lasted $9+4+2=15$ days, which means $15 \cdot 4=60$ student-catering assignments were necessary. Günther was assigned to 6 of these, so his group consisted of $\frac{60}{6}=10$ students.