What rate of interest does a man get for his money when in discounting a bill due in $10 \, \text{months}$, he deducts $4 \%$ of the amount of the bill? (in $\%$)

$1$ packet of biscuits costs $Rs.\, 16$,but a pack of $4$ of the same packets of biscuits costs $Rs.\, 56$. What is the effective discount (in $\%$) on the pack?

The true discount on a certain bill due for nine months at $4 \%$ simple interest is $Rs.\, 150$. Find the amount of the bill (in $Rs.$).

The true discount on a bill due $10$ months hence at $15 \%$ per annum is $Rs. 225$. The amount of the bill is (in $Rs.$)

If the true discount on $Rs. 161$ due for $2$ years and $6$ months is $Rs. 21$, then find the rate of interest (in $\%$).

The holder of a bill for $Rs. 17850$ nominally due on $May 21, 1991$ received $Rs. 357$ less than the amount of the bill by having it discounted at $5 \%$. When was it discounted?