Shortcut Trick
Apply Cross-Multiplication Method on Income and Expenditure ratios.
Income (7 : 5) and Expenditure (17 : 12) with savings (12000, 9000).
(7 × 12) − (5 × 17) units = (17 × 9000) − (12 × 12000)
|84 − 85| units = |153000 − 144000| ⇒ 1 unit = ₹9,000
Income of Seema = 7 × 9000 = ₹63,000; Darshan = 5 × 9000 = ₹45,000
Total Expenditure = (63000 − 12000) + (45000 − 9000) = 51000 + 36000 = ₹87,000
∴ The correct answer is ₹87,000.
Alternate Method
Given: Ratio of Income = 7 : 5, Savings = ₹12,000 and ₹9,000, Ratio of Expenditure = 17 : 12.
Formula Used: Income − Savings = Expenditure
⇒ Let the incomes be 7x and 5x.
⇒ (7x − 12000) / (5x − 9000) = 17 / 12
⇒ 12(7x − 12000) = 17(5x − 9000)
⇒ 84x − 144000 = 85x − 153000
⇒ x = 153000 − 144000 = 9000
⇒ Seema Expenditure = 7(9000) − 12000 = 51000
⇒ Darshan Expenditure = 5(9000) − 9000 = 36000
⇒ Total Expenditure = 51000 + 36000 = 87000
∴ The correct answer is ₹87,000.
Additional Information
Income-Expenditure Relationship
The fundamental relation is Income = Expenditure + Savings. Ratio problems can be solved by assuming a variable for either income or expenditure.
Cross-Multiplication Technique
Used when two ratios and the absolute changes (savings/additions) are given: (a:b) → (c:d) with changes m and n, then 1 unit = |dm − bn| / |ad − bc|.
Ratio Balancing
If savings were equal, the difference between ratio parts of income and expenditure could be equated by multiplying the ratios by the difference of the other ratio.