Two trains, A and B, start simultaneously from two stations $300\ \text{km}$ apart. Train A travels at $60\ \text{km/h}$, and Train B travels at $90\ \text{km/h}$. If a bird starts flying from Train A towards Train B at $120\ \text{km/h}$ and immediately turns back upon reaching Train B, continuing this until the trains meet, what total distance does the bird cover?
Time for trains to meet $= \dfrac{300}{60+90} = 2\ \text{h}$.
Bird flies the whole time at $120\ \text{km/h}$, so distance $= 120 \times 2 = 240\ \text{km}$.