One-fifth of a journey is covered at a speed of 30 km/h, one-fourth of the journey at a speed of 25 km/h and the rest at 60 km/h. What is the average speed (in km/h, correct to one decimal place) for the whole journey?

38.7

Let total distance = 200 km

\(\frac{1}{5}\)th of 200 = 40 km

Time 1 = \(\frac{40}{30}\)  = \(\frac{4}{3}\) hours

\(\frac{1}{4}\)th of 200= 50 km

Time 2 = \(\frac{50}{25}\) = 2 hours

Remaining distance = 200 - 40 - 50 = 110 km

Time 3 = \(\frac{110}{60}\) =  \(\frac{11}{6}\) hours

Total time = \(\frac{4}{3}\) + 2 + \(\frac{11}{6}\) = \(\frac{31}{6}\) hours

Average speed = \(\frac{200 × 6 }{31}\)  = 38.7 km/h