Time, Speed and Distance for Placement Aptitude

Time, Speed and Distance for Placement Aptitude

Speed, time, and distance problems appear in virtually every placement aptitude test in India. From simple distance calculations to complex train and boat problems, this topic rewards students who understand relative speed and can apply it quickly under exam conditions.

Fundamental Relationships

Distance equals Speed multiplied by Time. All problems in this chapter are variations of this one equation. To convert km per hour to metres per second, multiply by 5 divided by 18. To convert metres per second to km per hour, multiply by 18 divided by 5. Forgetting to convert units is one of the most costly errors in placement tests because it produces a wrong answer even with correct reasoning.

Average Speed and Relative Speed

For equal distances at speeds x and y, average speed equals 2xy divided by x plus y (harmonic mean, not arithmetic mean). When two objects move in opposite directions, their relative speed equals the sum of their speeds. When they move in the same direction, relative speed equals the absolute difference. For boats: downstream speed equals boat speed plus stream speed; upstream equals boat speed minus stream speed.

Solved Example

A train 240 metres long passes a pole in 12 seconds. How long to pass a 360-metre platform? Speed equals 240 divided by 12, which is 20 metres per second. Total crossing distance equals 240 plus 360, which is 600 metres. Time equals 600 divided by 20, which is 30 seconds.

Interview Tips

Train crossing problems follow a fixed pattern — always identify what is moving and add all relevant lengths. The average speed trap (arithmetic mean instead of harmonic mean) appears in almost every placement exam. Boat speed in still water equals downstream plus upstream divided by 2. Stream speed equals downstream minus upstream divided by 2. Memorize these two formulas and boat problems become straightforward.