Quantitative Aptitude
Quantitative Aptitude
SRCC GBO's quantitative section rewards fluency with arithmetic and the ability to translate a word problem into one or two equations. Core areas are number system, percentages, ratio and proportion, profit and loss, simple and compound interest, time-speed-distance, time and work, averages and mixtures, algebra, mensuration, and basic permutation, combination, and probability.
Core rules
- Percentage multipliers: an increase of 20% is x1.20; a decrease of 20% is x0.80. Successive changes multiply, they do not add.
- Time and work: take total work as the LCM of the given days, convert each worker to units per day, then add rates.
- Speed: 1 km/h = 5/18 m/s; for a train crossing a platform, distance = train length + platform length.
- Ratio: convert every quantity to the same base before comparing.
Worked example
A trader marks an article 40% above cost and then allows a 25% discount. What is his profit percent? Let cost = 100. Marked price = 140. Selling price = 140 x 0.75 = 105. Profit = 5 on 100 = 5%. The trap is to subtract 40% - 25% = 15%, which is wrong because the discount applies to the marked price, not the cost.
Traps that cost marks
- Confusing percentage points with percent change.
- Applying discount to cost instead of marked price.
- Mixing simple and compound interest in the same problem.
- Forgetting unit conversions (minutes to hours, cm to m).
- Rounding too early; carry exact fractions until the final step.