## 12. Convoy of Ships

In 1943, in one American port, there were four escort ships, seven cargo ships, and three aircraft carriers. From these ships, a transport convoy was formed to deliver food and ammunition to Europe. At the head was an escort ship, followed by three cargo ships, then an aircraft carrier, and lastly, another escort ship.

In how many different ways can such a convoy be organized?
12. The number of ways to choose the first escort ship is 4. The selection of three cargo ships can be carried out

$$
C_{3}^{3}=\frac{7!}{3!4!}=35
$$

ways.

The number of ways to choose an aircraft carrier is 3. The last escort ship can be chosen in 3 ways (since only three unused ships remain).

Thus, there are $4 \cdot 35 \cdot 3 \cdot 3=1260$ ways to form the transport heading to Europe.