How Much Time Did the Cyclist Spend Cycling? Unlocking the Math Behind a 120 km Dual-Walk & Cycle Journey

If you’ve ever wondered how time is split when someone covers 120 km using equal walking and cycling segmentsβ€”like cycling for part of the distance and walking the restβ€”this article breaks down the physics and math behind the scenario. In one compelling example, a cyclist covers 120 kilometers in exactly 4 hours, alternating cycling and walking. With cycling speed at 30 km/h and walking at 5 km/h, how many minutes did they spend actually cycling?


Understanding the Context

The Challenge: 120 km in 4 Hours with Equal Segments

Imagine a cyclist who splits their journey into two equal parts: 60 km cycling and 60 km walking, resulting in a total time of 4 hours. With cycling speed at 30 km/h, and walking at 5 km/h, we want to calculate the exact time spent cycling.


Step 1: Calculate Time Cycling and Walking in Equal Distances

Key Insights

Let:

  • Distance cycled = 60 km
  • Distance walked = 60 km
  • Cycling speed = 30 km/h
  • Walking speed = 5 km/h

Time = Distance Γ· Speed

  • Time spent cycling = 60 km Γ· 30 km/h = 2 hours
  • Time spent walking = 60 km Γ· 5 km/h = 12 hours

Waitβ€”this adds to 14 hours, not 4! So clearly, the equal distance assumption doesn’t match the time constraint.


Final Thoughts

Step 2: Adjust for Total Time = 4 Hours

We know total time = 4 hours.
Let the distance cycled = x km
Then distance walked = 120 – x km

Time cycling = x Γ· 30
Time walking = (120 – x) Γ· 5

Total time:
(x/30) + ((120 – x)/5) = 4 hours

Now solve for x:

Multiply through by 30 to eliminate denominators:

x + 6(120 – x) = 120

Expand:
x + 720 – 6x = 120

Combine like terms:
-5x + 720 = 120

-5x = 120 – 720 = –600