Railways Notes / Mathematics (Quantitative Aptitude) / Chapter 14
Chapter 14 of 31

Time, Speed and Distance

The core Speed = Distance/Time relationship, unit conversion, and relative speed — the base for Boats & Streams and Trains.

📖 ~4 min read 📐 RRB NTPC / Group D — Mathematics

Core Formula

Speed = Distance ÷ Time

Unit Conversion

  • km/hr to m/s: multiply by 5/18
  • m/s to km/hr: multiply by 18/5

Relative Speed

DirectionRelative Speed
Same directionDifference of speeds
Opposite directionSum of speeds

Average Speed (equal distances)

Average Speed = 2×S1×S2 / (S1+S2) — applies ONLY when the two distances covered are equal.
💡 Example: A travels at 40 km/hr, returns at 60 km/hr. Average speed = 2×40×60/(40+60) = 48 km/hr (not the plain average of 50).

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