Let the monthly expenditures of A be 2x ⇒ 2x = 8000 ⇒ The monthly expenditure of B = 3x = Rs. 12000 ⇒ The monthly saving of A = monthly income of A – monthly expenditure of A ⇒ The monthly saving of A = 12000 – 8000 = Rs. 4000 ⇒ The monthly saving of B = 15000 – 12000 = Rs. 3000 ⇒ The sum of their monthly savings = 4000 + 3000 = Rs.7000 ∴ The sum of their monthly savings is 7000 rupees.