The interest on a certain sum of money is Rs. 67.20 and the discount on the same of money for the same time and at the same rate is Rs. 60. What is sum?

Interest on Sum - True discount
= Interest on true Discount.
Proof Sum = P.W. + T.D.
∴ Interest on Sum = Interest on P.W. + Interest on T.D.
= T.D. + Interest on T.D.
Interest on Sum - T.D. = Interest on T.D. or Banker's gain = Int. on T.D.
Rs. 67.20 - Rs. 60 = Interest on Rs. 60
∴ Rs. 7¹/₅ = Interest on Rs. 60
∴ Re.1 = Interest on Rs. 60/7¹/₅
∴ Rs. 67¹/₅ = Interest on Rs. 60 / 7¹/₅ x 67¹/₅
∴ The required sum = Rs. 60/7¹/₅ x 67¹/₅ = Rs. 560