4. Katrin arranges tables measuring $2 \mathrm{~m}$ by $1 \mathrm{~m}$ according to the number of participants in a meeting. The diagrams show the plan view for a small, a medium and a large meeting.
How many tables are needed for a large meeting?
A 10
B 11
C 12
D 14
E 16
Solution
C

Every $7 \mathrm{~m}$ length of the square consists of one $1 \mathrm{~m}$ edge of a table and three $2 \mathrm{~m}$ edges. Thus every side of the square uses three tables, and Katrin needs $4 \times 3=12$ tables altogether.