Arithmetic and Mental Ability
Speed and accuracy
Cover percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, mensuration, data interpretation, number series, coding-decoding, blood relations, directions, and syllogisms. Learn tables up to 20, squares up to 30, and common fraction-percentage equivalents.
Traps
Unit conversion is the biggest trap: to change km/h to m/s, multiply by 5/18. Successive percentage changes are not additive. Average speed is total distance divided by total time, not the mean of two speeds. In interest, check whether the question uses SI or CI and whether time is in months.
Rule of thumb
Write the formula, substitute with units, and check whether the answer is plausible. In series, test differences first, then ratios, then squares or cubes. In blood relations, draw a family tree; in directions, draw axes.
Worked example
Two successive discounts of 20% and 10% on ₹1,000. After 20%, the price is ₹800; after 10%, it is ₹720. The total discount is ₹280, or 28%, not 30%. Formula: net discount = 100 − (100−20)(100−10)/100 = 28%.
Data interpretation
Read the axes and units before calculating. Approximate to eliminate options when the choices are far apart, but calculate exactly when they are close.