Questions
3 questions per paper
Difficulty
Medium
Importance
High yield for SSC CGL/CHSL
Overview
Time, Speed, and Distance is a fundamental pillar of quantitative aptitude that tests your ability to manipulate variables in motion-based scenarios. Mastering this is crucial for SSC and banking exams as it forms the basis for complex data interpretation and arithmetic word problems.
Relative Speed
Relative speed determines how fast two objects move in relation to each other, a concept vital for overtaking or collision problems. Always observe the direction of travel, as it dictates whether you add or subtract individual speeds.
- Same direction: Speed = |S1 - S2|
- Opposite direction: Speed = S1 + S2
- Conversion: m/sec to km/hr = multiply by 18/5
- Conversion: km/hr to m/sec = multiply by 5/18
Trains and Platforms
Train problems require calculating the total distance covered when crossing an object with length, such as a platform or another train. Remember to include the train's own length in the total distance calculation.
- Distance = L(train) + L(platform/bridge)
- Crossing a stationary pole: Distance = L(train)
- Crossing a moving person: Use relative speed logic
- Time taken = (Length1 + Length2) / Relative Speed
Boats and Streams
This subtopic introduces the effect of water current on a boat's velocity. Treat downstream as movement with the current and upstream as movement against it, factoring in the stream speed.
- Downstream speed (v + u)
- Upstream speed (v - u)
- Speed of boat (v) = (Downstream + Upstream) / 2
- Speed of stream (u) = (Downstream - Upstream) / 2
Races and Circular Motion
Races introduce time-head starts and winner margins, requiring logical deduction alongside basic speed math. Circular tracks require finding the point and time of first meeting based on relative speeds.
- Meeting time on circular track (opposite) = Circumference / (S1 + S2)
- Meeting time on circular track (same) = Circumference / (S1 - S2)
- Race handicap: Adjust distance or time before calculation
- Ratio of speeds = Inverse ratio of time for same distance
Formula Sheet
Distance = Speed * Time
Average Speed = (Total Distance) / (Total Time)
Average Speed for equal distances = (2xy) / (x + y)
Relative Speed (Same Dir) = S1 - S2
Relative Speed (Opposite Dir) = S1 + S2
Speed of Boat = (Downstream + Upstream) / 2
Speed of Stream = (Downstream - Upstream) / 2
Exam Tip
Whenever the distance is constant, use the inverse proportionality of speed and time—Ratio of speeds = (1/T1 : 1/T2)—to bypass heavy algebraic steps.
Common Mistakes
- Failing to convert all units into a consistent format (e.g., mixing km/hr with seconds).
- Forgetting to include the train's length when calculating the distance required to cross a tunnel or platform.
- Misinterpreting upstream and downstream variables in complex boat-stream algebraic equations.
More Revision Notes
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