The monthly income of two persons is in the ratio 4:5 and their expenditures are in the ratio 7 : 9. If each saves ₹50 per month, then their monthly incomes are:

₹400; ₹500

Income = Expenditure + Savings.

⇒                 A   :   B

Income         4   :   5

Expenditure   7   :   9

⇒ To make difference between A and B in both ratio, we multiply income ratio with 2,

⇒ (4 : 5) x 2 = 8 : 10.

⇒ Income - Exp. = Savings

       8  : 10

       7  :  9

       1  :  1

⇒ 1 unit = Rs. 50.

⇒ Income of A and B = 8 x 50 = Rs.400, 10 x 50 = Rs.500