Shortcut Trick
Ratio of Initial Income : Expenditure : Savings = 16500 : 12000 : 4500 ⇒ 11 : 8 : 3.
Using the weighted average method: (Total Ratio × Income Change) = (E_ratio × Expenditure Change) + (S_ratio × Savings Change)
11 × 24 = 8 × (−10) + 3 × x
264 = −80 + 3x ⇒ 3x = 344 ⇒ x = 114.66%
Rounding off to the nearest integer, we get 115%.
∴ The correct answer is 115%.
Alternate Method
Given:
Initial Income = ₹16,500
Initial Expenditure = ₹12,000
⇒ Initial Savings = Income − Expenditure = 16,500 − 12,000 = ₹4,500
Calculations:
⇒ New Income = 16,500 + (24% of 16,500) = 16,500 × 1.24 = ₹20,460
⇒ New Expenditure = 12,000 − (10% of 12,000) = 12,000 × 0.90 = ₹10,800
⇒ New Savings = New Income − New Expenditure = 20,460 − 10,800 = ₹9,660
⇒ Increase in Savings = 9,660 − 4,500 = ₹5,160
⇒ Percentage Increase = (Increase ÷ Initial Savings) × 100
⇒ Percentage Increase = (5,160 ÷ 4,500) × 100 = 114.66%
⇒ Percentage Increase ≈ 115% (rounded off to the nearest integer)
∴ The correct answer is 115%.
Additional Information
Income, Expenditure, and Savings Relationship
Income = Expenditure + Savings. Any absolute change in income is exactly equal to the sum of absolute changes in expenditure and savings.
Percentage Change Formula
Percentage Change = [(Final Value − Initial Value) ÷ Initial Value] × 100. A positive value represents a growth/increase while a negative value signifies a reduction.
Weighted Average Method for Change
If an entity is divided into two parts, the overall percentage change is the weighted average of the changes of its parts: Total % Change = (R1 × C1 + R2 × C2) ÷ (R1 + R2), where R represents the ratio and C represents the percentage change.