Mathematics and Numerical Reasoning
Mathematics and Numerical Reasoning tests accurate calculation and the ability to choose the right model. Topics include ratio, percentage, interest, time and work, algebra, geometry, mensuration and basic statistics. Show steps; a correct answer with no reasoning may still lose marks in a written paper. Substitute answers back to verify when time allows.
Core rules
- Percentage change uses the original base unless stated otherwise.
- Successive discounts multiply factors: 20% then 10% = 0.8 × 0.9, not 30% off.
- Simple interest = P × R × T / 100; compound interest grows on the new amount.
- Ratio: convert to the same unit before comparing.
- Mensuration: area and volume formulas must use consistent units.
Worked example
A shirt costs Rs 1,200. A 20% discount is given, then 10% off the reduced price. Reasoning: first discount = 0.8 × 1,200 = 960. Second discount = 0.9 × 960 = 864. Final price = Rs 864. The total discount is 336/1,200 = 28%, not 30%. The trap is adding the two percentages.
Traps
Adding successive percentages; using the new price as the base for a percentage increase; mixing cm and m; forgetting order of operations; rounding too early; misreading ‘at least’ as ‘more than’.