Quantitative Aptitude and Elementary Mathematics
Scope
The section covers the number system, HCF-LCM, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time-work and pipes, time-speed-distance including trains, mensuration, and table or graph interpretation. Expect short, calculation-light questions where the method matters more than the arithmetic.
High-yield rules
- Successive percentage change: net = a + b + ab/100.
- Trains: distance covered = train length plus platform length (or plus the other train's length); convert km/h to m/s by multiplying by 5/18.
- Relative speed: subtract for same direction, add for opposite direction.
- Time and work: convert to one-day work, then add reciprocals.
- SI = PRT/100; CI amount = P(1 + r/100)^n.
Worked example
A 240 m long train runs at 72 km/h. How long does it take to clear a 360 m platform? Step 1: 72 × 5/18 = 20 m/s. Step 2: the engine must travel its own length plus the platform, so 240 + 360 = 600 m. Step 3: time = 600/20 = 30 seconds. Check: crossing a mere pole would take 240/20 = 12 s, so 30 s is consistent for a platform.
Traps that cost marks
- Using the train length alone and forgetting the platform or second train.
- Adding speeds when two trains run in the same direction.
- Taking percentage on the wrong base: a 20% rise then a 20% fall gives a net 4% fall, not zero.
- Leaving the answer in m/s when the options are in km/h.
- In data interpretation, reading a percentage of total as a raw count.