The incomes of A and B are in the ratio 5 : 3, their expenditures are in the ratio 8 : 5 and their savings are in the ratio 2 : 1. If their total savings of a year is Rs. 3600. Find the monthly income of A.

Let A's and B's income be 5y and 3y respectively and their expenditure be 8z and 5z respectively.

Let their savings be 2x and x respectively

2x + x = 3600

3x = 3600

x = 1200

now,

5y – 8z = 2x

5y – 8z = 2400          (1)

3y – 5z = x

3y – 5z = 1200          (2)

Multiply eq (1) by 5 eq (2) by 8 and subtract eq (2) from eq (1) on solving we get,

y = 2400

Hence  A's income  $=5y=5\times 2400=\frac{12000}{12}=1000$