If the cost of $1$ dozen bananas is $Rs.48$ then the cost of $5$ such bananas is:

The correct option is D $Rs.20$

We know that $1$ dozen $=12$ units

Therefore, if cost of $1$ dozen bananas is $Rs.48$, then

CP of $12$ bananas $=Rs.48$

Therefore, CP of $1$ banana $=\frac{Rs.48}{12}=Rs.4$

Hence, CP of $1$ bananas $=4\times 5=Rs.20$