Mathematics: Speed, Accuracy, and Shortcuts
Core Concepts
Mathematics for Navik GD typically covers arithmetic: number system, HCF/LCM, percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time-speed-distance, time and work, mensuration, and basic algebra and geometry. The exam rewards speed, so mental calculation and standard formulas matter more than long derivations.
Traps to Watch
Percentage questions often reverse the base: a 20% increase followed by a 20% decrease does not return to the original value. In time and work, remember that rates add, not times. In profit and loss, always compute percentage on cost price unless stated otherwise. For compound interest, the number of compounding periods and the rate per period must match. Units in mensuration (cm vs m) are a frequent source of error.
Rule of Thumb
Use the unitary method as a universal fallback: reduce every problem to a per-unit rate, then scale. For successive percentage changes, use the combined formula a + b + ab/100.
Worked Example
A shopkeeper marks an item 40% above cost and gives a 25% discount. Find the profit percentage. Let cost = 100. Marked price = 140. Selling price = 140 x 0.75 = 105. Profit = 5 on 100, so 5%. Using the formula: 40 + (-25) + (40 x -25)/100 = 15 - 10 = 5%.