Quantitative Aptitude / Numerical Ability
Syllabus weight
Numerical Ability in MSC Bank papers is speed-based: simplification and approximation, number series, percentage, ratio, average, time-work, time-speed-distance, simple and compound interest, profit-loss, mixtures, probability, and data interpretation through tables, bar charts and pie charts. Most questions are class 10 level; the challenge is choosing the shortest method.
Rules to internalise
- BODMAS: brackets, orders, division/multiplication, addition/subtraction.
- Learn fraction-percentage equivalents: 1/8 = 12.5%, 1/6 = 16⅔%, 3/8 = 37.5%.
- Successive percentage change: net = a + b + ab/100.
- Compound interest: A = P(1 + r/100)^n; simple interest = PRT/100.
- Work: if A finishes in x days and B in y, together they take xy/(x+y) days.
- In data interpretation, identify the base before calculating a percentage change.
Worked example
A can complete a task in 12 days and B in 18 days. How long will they take together? Take total work as LCM(12,18) = 36 units. A does 3 units/day, B does 2 units/day. Combined rate = 5 units/day. Time = 36/5 = 7.2 days, i.e. 7 days 4.8 hours. Alternative: 12×18/(12+18) = 216/30 = 7.2 days.
Traps
Approximating when the options are close; using the old value as the denominator in percentage-change questions; forgetting that successive discounts use the reduced price; and mixing SI and CI for periods longer than one year. In DI, read whether the question asks for absolute increase or percentage increase.