A bill is discounted at 10% per annum. If banker's discount is allowed, at what rate percent should the proceeds be invested so that nothing will be lost?

Answer: Option B

Let the amount = Rs. 100
Then BD = Rs.10 (∵ banker's discount, BD is the simple Interest on the face value of the bill for unexpired time and bill is discounted at 10% per annum)
Proceeds = Rs. 100 - Rs. 10 = Rs. 90
Hence we should get Rs. 10 as the interest of Rs. 90 for 1 year so that nothing will be lost
$$\begin{array}{rl}& \Rightarrow 10=\frac{90\times 1\times R}{100}\\ & \Rightarrow R=\frac{10\times 100}{90}\\ & =\frac{100}{9}\\ & =11\frac{1}{9}\%\end{array}$$