(b) Let monthly incomes of A and B be 7 x and 10 x respectively and their expenditures be 2 y and 3 y respectively.
According to the question, ⇒ 7x - 2y = 1000 .......(i) and 10x - 3y = 1000 .......(ii) Multiplying by of Eq. (i) and by Eq (ii) and subtracting ⇒ 21x - 6y = 3000 ......(i) ⇒ 20x - 3y = 2000 .......(ii) --- + --- ⇒ x=1000 ∴ Mostly income of B = 10 × 1000 = Rs 10000