The income of B is 85% of A and income of C is Rs 3600

Solution

Let the income of A be Rs 100a  Than, income of B is = 100 x 0.85a = Rs 85a  income of C = Rs (85a + 3600)  income of A+B+C = 100a + 85a + 3600 = 270a + 3600   Now , 270a + 3600 = 8400 x 3             270a = 21600              a=80  earning of A= 8000 ;  B = 6800 ;  C = 10,400  Savings of A= 8000 x  ½  = 4000 Savings of B = 6800 x ½ = 3400  Therefore avg savings of A and B = (4000+3400)/2 = Rs 3700  Let savings of C be k  Therefore expenditure of C be k+780  Now, k + k + 780 = 10400            2k = 9620             K = 4810  Therefore the  % will be = 4810/3700 x 100 = 130%