DRDO Multi tasking staff Model paper 4

Let their monthly incomes be 5x and 4x.
⇒ Let their monthly expenditures be 9y and 7y respectively.
Given, money left after expenditures = 1000 for both sisters
⇒ 5x – 9y = 1000 and 4x – 7y = 1000
⇒ 5x – 9y = 4x – 7y
⇒ x = 2y
Substitute x = 2y in any one of the equations;
⇒ 10y – 9y = 1000 ⇒ y = 1000
⇒ x = 2y = 2000
∴ Their monthly incomes = 5x and 4x = 5 × 2000 and 4 × 2000 = 10000 and 8000