Question
The ratio of incomes of A and B is 5 : 7. Each of them
saves Rs 600 per month. The ratio of their expenditures is 3 : 5. What is B's monthly income?Solution
Let incomes of A and B be 5k and 7k respectively. Let their monthly expenditures be 3m and 5m respectively. Savings = Income − Expenditure For A: 5k − 3m = 600 …(1) For B: 7k − 5m = 600 …(2) From (1): 3m = 5k − 600 From (2): 5m = 7k − 600 m from (2): m = (7k − 600)/5 Substitute in (1): 3 × (7k − 600)/5 = 5k − 600 (21k − 1800)/5 = 5k − 600 21k − 1800 = 25k − 3000 −4k = −1200 → k = 300 B's income = 7k = 7 × 300 = 2100 Answer = Rs 2100
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