Arithmetic and Numerical Ability
What this domain tests
This section tests percentages, ratio and proportion, averages, simple and compound interest, profit and loss, time and work, speed and distance, mensuration and data interpretation. Accuracy depends on translating words into one clean equation.
Core formulas
- Percentage change = change/original x 100.
- Simple interest = P x R x T/100; compound amount = P(1 + R/100)^T.
- Profit% = profit/cost price x 100; discount is on marked price.
- Work: combined rate = sum of individual rates.
- Speed = distance/time; average speed is total distance divided by total time.
Worked example
A marked price of 1000 receives successive discounts of 20% and 10%. Find the final price and effective discount. Reasoning: after 20%, price = 800; after 10%, price = 800 x 0.9 = 720. Total discount = 280, so effective discount = 280/1000 x 100 = 28%, not 30%.
Traps that cost marks
Successive discounts do not add; compound interest exceeds simple interest after the first year; average speed is not the arithmetic mean of two speeds unless distances are equal. Convert units before dividing.