Quantitative Aptitude
Percentages, averages, speed and simple interest.
6 min read · currentaffairschronicle.com editorial
Percentages
To find x% of a value, multiply by x and divide by 100. A 10% increase followed by a 10% decrease does not return the original — it leaves a 1% loss. Practise successive percentage changes.
Averages
The average of a set is the sum divided by the count. If a new value equals the average, the average is unchanged; if it differs, the average shifts accordingly. Use the deviation method for speed.
Speed, time and distance
Speed = distance ÷ time. For trains, remember to add the length of the train. For relative speed, objects moving in the same direction have speeds subtracted; opposite directions have speeds added.
Simple and compound interest
Simple interest = principal × rate × time ÷ 100. Compound interest grows faster because interest earns interest. Know the formula A = P(1 + r/100)ⁿ for amount after n years.