General Mathematics / Quantitative Aptitude
What is tested
Numerical ability at the level of percentages, ratios, averages, profit and loss, simple and compound interest, time–work, time–speed–distance, mensuration, and data interpretation from tables, bar charts and pie charts. Speed comes from memorising standard fraction–percentage equivalents.
Core rules
- Percentage change is always computed on the original (base) value.
- Successive changes: net change = a + b + ab/100.
- Profit/loss is calculated on cost price; discount is calculated on marked price.
- Time and work: invert rates; take the LCM of the given days as total work units.
- Speed: convert km/h to m/s by multiplying by 5/18.
- Averages: total = average × number of terms; avoid averaging already-averaged figures.
Worked example
A shopkeeper marks an article 40% above cost and allows a 25% discount. What is the profit percentage? Let cost = 100. Marked price = 140. Discount = 25% of 140 = 35, so selling price = 105. Profit = 5 on a cost of 100, i.e. 5%. The common error is 40 − 25 = 15, which ignores that the discount acts on the marked price, not the cost.
Traps
- Applying discount to cost price instead of marked price.
- Mixing simple and compound interest - CI compounds annually unless stated otherwise.
- In time–work, adding days instead of rates when a worker leaves midway.
- Ratio questions where the total is not 100: use a common multiplier instead of assuming percentages.