11. In one class, there are fewer than 50 students. On Gorky Street, $\frac{1}{7}$ of the students from this class live, on Pushkin Street - $\frac{1}{3}$, on Gaidar Street - $\frac{1}{2}$, and on Shipbuilding Street - the remaining students. How many students live on Shipbuilding Street?
11. The number of students in the class must be a multiple of the numbers 7, 3, and 2. The least common multiple of these numbers is $42(7 \cdot 3 \cdot 2=42)$. It is less than 50, so it satisfies the condition. Then $42 \cdot \frac{1}{7}=6 ; 42 \cdot \frac{1}{3}=14 ; 42 \cdot \frac{1}{2}=21$; $42-(6+21+14)=1$. Therefore, 1 student of this class lives on Shipbuilding Street.