When a bank reduce the rate of interest from 6 1/ 2% per annum to 5 1/ 2% per annum, depositor withdrew Rs. 600 and thereby his interest reduced by ₹ 73. Find the initial deposit.?

Initially ,
let P = ₹ A, R = 13/2% per annum and T = 1yr
SI = PRT/100 = (A x 1 x 13/2)/100 = ₹ 13A/200
Now, new deposit = ₹ (A - 600), R = 11/2 % per annum and T = 1yr
SI = PTR/100 = [(A - 600) x 1 x 11/2)/100] = ₹ 11(A - 600)/200
By the given condition ,
13A/200 - 11(A - 600)/200 = 73
⇒ 13A - 11(A - 600 ) = 200 x 73
⇒ 2A = 200 x 73 - 600 x 11
⇒ 2A = 14600 - 6600
⇒ 2A = 8000
∴ A = 4000
Hence, the initial investment is ₹ 4000.