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

Rs.400; Rs.500

                       I   :  II

Income           4   :   5

Expenditure    7   :   9

___________________

Savings =   -50     -50            (Income - Expenditure)

$\frac{4R\;-\;50}{5R\;-\;50} = \frac{7}{9}$

Using cross - multiplication method, 

⇒ 36R - 35R = (-50 x 7) - (-50 x 9)

⇒              R = 100

Their income = 400, 500