## Task 4 - 250734

A fighter jet flew $200 \mathrm{~km}$ further in half an hour than a sports plane in one hour. How great was the speed of each of these two aircraft, if the speed of the fighter jet was three times as great as that of the sports plane?
The speed of the sports plane is $x \frac{\mathrm{km}}{\mathrm{h}}$, and that of the fighter plane is then $3 x \frac{\mathrm{km}}{\mathrm{h}}$. Since the sports plane flew $x \mathrm{~km}$ in one hour, the fighter plane flew $(x+200) \mathrm{km}$ in half an hour and therefore $2 \cdot(x+200) \mathrm{km}$ in one hour. Thus, we have

$$
3 x=2 \cdot(x+200) \quad \Rightarrow \quad x=400
$$

The sports plane thus had a speed of $400 \frac{\mathrm{km}}{\mathrm{h}}$, and the fighter plane had a speed of $1200 \frac{\mathrm{km}}{\mathrm{h}}$.