A girl travels 30 km at a speed of 15 km/h. She travels another 20 km at a speed of 10 km/h. What is her average speed for the entire journey?

12.5 km/h

Average Speed = \(\frac{Total\; Distance }{Total\; Time }\)

Distance = Speed × Time

Total distance = 30 + 20 = 50 km

Total time =   \(\frac{30 }{15 }\) +   \(\frac{20 }{10 }\) =   4 hours

Average speed =   \(\frac{50  }{4 }\) = 12.5 km/h