Shortcut Trick
Use the Cross-Multiplication Method for the Income ratio (5 : 8) and Savings ratio (3 : 4) with given Expenditures.
Difference in cross-products of ratios: |(5 × 4) − (8 × 3)| = |20 − 24| = 4 units.
Difference in cross-products of values: |(3 × 60,000) − (4 × 36,000)| = |180,000 − 144,000| = 36,000.
4 units = ₹36,000 ⇒ 1 unit = ₹9,000.
Income of B = 8 units × 9,000 = ₹72,000.
Savings of B = Income − Expenditure = 72,000 − 60,000 = ₹12,000.
∴ The correct answer is ₹12,000.
Alternate Method
Given:
Ratio of Incomes of A and B = 5 : 8
Expenditure of A = ₹36,000 | Expenditure of B = ₹60,000
Ratio of Savings of A and B = 3 : 4
Formula Used:
Income − Expenditure = Savings
Calculations:
Let the Incomes of A and B be 5x and 8x respectively.
⇒ Savings of A = 5x − 36,000
⇒ Savings of B = 8x − 60,000
⇒ (5x − 36,000) / (8x − 60,000) = 3 / 4
⇒ 4 × (5x − 36,000) = 3 × (8x − 60,000)
⇒ 20x − 144,000 = 24x − 180,000
⇒ 24x − 20x = 180,000 − 144,000
⇒ 4x = 36,000
⇒ x = 9,000
⇒ Savings of B = 8 × 9,000 − 60,000
⇒ Savings of B = 72,000 − 60,000 = 12,000
∴ The correct answer is ₹12,000.
Additional Information
Income-Expenditure Relationship
The fundamental equation for financial problems is Income = Expenditure + Savings. If any two ratios are given along with absolute values of the third component, the variables can be solved linearly.
Cross-Multiplication Method
For equations of the form (ax − c)/(bx − d) = m/n, the shortcut is |an − bm| units = |nd − mc|. This directly helps in finding the common multiplier 'x'.
Ratio Scaling
Ratios can be scaled by a constant factor without changing the relationship. In income problems, ensure the multiplier is applied to the base income ratio before calculating individual savings or expenditures.