A travels 15 km with a speed of 30 km/h. He travels another 25 km with a speed of 10 km/h. What is his average speed for the entire journey?

$\frac{40}{3}$km/h

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

Distance = Speed × Time

Total distance = 15 + 25 = 40 km

Total time =   \(\frac{15 }{30 }\) +   \(\frac{25 }{10 }\) =   3 hours

Average speed =   \(\frac{40  }{3 }\) km/h