Numerical and Mental Ability (Mathematics)
What this section tests
This domain covers simplification and BODMAS, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time–speed–distance, time and work, mensuration and data interpretation. Speed matters: most items are solvable in under a minute once the base is fixed correctly.
Core rules
- Percentage change = (change ÷ original) × 100; successive discounts of a% and b% equal a + b − ab/100.
- Profit and loss are calculated on cost price; discount is calculated on marked price.
- Simple interest = P × R × T ÷ 100. Compound interest compounds yearly unless stated otherwise.
- Time and work: convert days to work-per-day (a man finishing in 12 days does 1/12 per day), add rates, then invert.
- Average = sum ÷ count; if every value rises by k, the average rises by k.
Worked example
Question: A shopkeeper marks an article 40% above cost price and allows a 25% discount. Find his profit percentage.
Step 1: Take cost price = ₹100, so marked price = ₹140. Step 2: Discount is on the marked price: 25% of 140 = ₹35, hence selling price = ₹105. Step 3: Profit = 105 − 100 = ₹5 on a cost of ₹100, so profit = 5%. The whole problem collapses once cost price is taken as 100.
Traps that cost marks
- Applying the discount to cost price instead of marked price.
- Mixing speed units: km/h to m/s needs × 5/18.
- Using simple interest where the question says compounded annually.
- Ignoring unit changes in mensuration (cm to m) before computing area or volume.
- Rounding early; carry fractions until the final step.