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?

Given

Distance1 = 15 km, Speed1 = 30 km/h

Distance2 = 25 km, Speed2 = 10 km/h

Formula Used:

Speed = Distance/Time

Average speed = Total distance/Total time

Calculation:

According to the question,

Total distance = 15 + 25 = 40 km

Total time = 15/30 + 25/10

⇒ (15 + 75)/30 = 90/30 = 3 hours

Average speed = 40/3 km/h

∴ The average speed for the entire journey is 40/3 km/h.

Given 

D₁ = 15 km, S₁ = 30 km/h

D₂ = 25 km, S₂ = 10 km/h

Formula Used:

Average speed = \(\frac{{{D_1} + {D_2}}}{{\frac{{{D_1}}}{{{S_1}}} + \frac{{{D_2}}}{{{S_2}}}}}\)

Calculation:

Average speed for the entire journey = \(\frac{{15 + 25}}{{\frac{{15}}{{30}} + \frac{{25}}{{10}}}}\)

\(= \frac{{40}}{{0.5 + 2.5}}\)