General Mathematics / Quantitative Aptitude
General Mathematics in JSSC CGL is arithmetic-led. The paper usually tests percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, time-speed-distance, mensuration and data interpretation. The questions are standard, so speed comes from mastering a small number of shortcut relations rather than from exotic formulas.
Formula anchors
- Profit percentage is always calculated on cost price unless the question says otherwise; loss percentage likewise on cost price.
- Compound interest for two years equals simple interest for two years plus the interest on the first year's interest.
- For time and work, convert days into one-day work rates: if A finishes in x days, A does 1/x of the work per day.
- Average = total ÷ count; if every value rises by k, the average rises by k.
Worked example
A can finish a task in 12 days and B in 18 days. Working together, how long do they take? Reasoning: take the LCM of 12 and 18, which is 36, as the total work in units. A does 36 ÷ 12 = 3 units per day, B does 36 ÷ 18 = 2 units per day. Together they do 5 units per day, so time = 36 ÷ 5 = 7.2 days, that is 7⅕ days. Answer: 7⅕ days.
Traps that cost marks
- Applying a percentage increase and then a percentage decrease of the same rate - the result is never the original value.
- Mixing simple and compound interest in the same question.
- Forgetting unit conversion: km/h with metres, minutes with hours, centimetres with metres.
- Reading a data-interpretation table without checking whether the values are in thousands or lakhs.