Reasoning and Quantitative Aptitude: Speed With Accuracy
Reasoning and quantitative aptitude is a speed section: the questions are school-level, but the cut-off is decided by accuracy under time. Learn the shortcuts and, equally, the exact points where approximation becomes unsafe.
Quant core areas
Percentages and ratios (convert everything into fractions), simple and compound interest, time-speed-distance, time and work, mixtures and alligation, averages, profit and loss, permutations and combinations, mensuration, and data interpretation in table, bar, pie and caselet form.
Reasoning core areas
Number and letter series (difference, product, square and cube patterns), coding-decoding, blood relations, direction sense, syllogism through Venn diagrams, linear and circular seating, multi-variable puzzles, inequality and input-output.
Worked example
A sum doubles in 8 years at simple interest. Doubling means 100% interest in 8 years, so the rate is 100/8 = 12.5% per annum. To become four times, the interest needed is 300%, so time = 300/12.5 = 24 years. The linear shortcut works only for simple interest; under compound interest the same sum would quadruple in 16 years, which is exactly why the question must specify SI before you commit to an answer.
Traps
- Mixing percentage increase with percentage points.
- Taking average speed as the arithmetic mean of two speeds instead of total distance over total time.
- In data interpretation, mixing units (lakh versus crore) or taking a percentage of a percentage.
- In puzzles, ignoring one negative clue that eliminates two arrangements at once.