A library has an average of 510 visitors on Sundays and 240 on other days. The average number of visitors per day in a month of 30 days beginning with a Sunday is:

Answer: Option D

Since the month begins with a Sunday, to there will be five Sundays in the month.
$$\begin{array}{rl}& \therefore \text{Required}\text{average}\\ & =\frac{510\times 5+240\times 25}{30}\\ & =\frac{8550}{30}\\ & =285\end{array}$$