11) The banker’s discount on Rs. 1500 at 15% per annum is the same as the true discount on Rs. 1550 for the same time and the same rate. What is the time?

Bankers Discount, B.D. = Simple Interest on the face value of the bill for unexpired time. Tue Discount, TD = Simple Interest on the present worth or value for the unexpired time. S.I. on Rs. 1500 = T.D. on Rs. 1550 Rs. 1500 is the Present Worth or Value of Rs. 1550 Rs. 50 is the simple interest on Rs. 1500 at 15%

12) The bankers gain on a sum due 5 years hence at 14% per annum is Rs. 280. What is the banker’s discount?

15) A bill is discounted at 20% per annum. If the banker’s discount is allowed, at what rate percent should be proceeds be invested so that nothing will be lost?

So, B.D. = Rs. 20 as banker’s discount is the simple interest on the face value of the bill for the unexpired time and bill is discounted at 20% per annum.

Proceeds = Rs. 100 – Rs. 20 = Rs. 80

So, we should get Rs. 20 as the interest of Rs. 80 for one year so that nothing will be lost.