Delhi Police Constable Exam Model Paper 6

Tips & Tricks
Given:
Price of rifle depreciates 10% every year
Concept used
10% = 1/10
Calculation:
Every year price reduces by 10%m, that is, if at starting of year price = 10x then at the end of year price = 9x
⇒ For two years combined, Price at start $=10\mathit{x}\times 10\mathit{x}=100{\mathit{x}}^2,$ Price at end of 2 years = $9\mathit{x}\times 9\mathit{x}=81{\mathit{x}}^2$
∴ Price at start $=100{\mathit{x}}^2=\mathit{I}\mathit{N}\mathit{R}82000$
⇒ ${\mathit{x}}^2=$ INR 820
After 2 years, value of rifle becomes = 81x^2 = 81 × INR 820 = INR 66420
⇒ Value of rifle after 2 years = INR 66420
Short trick:
Value of rifle after 2 years = (9/10) × (9/10) × 82000
⇒ Value of rifle after 2 years = INR 66420