In this question, one has to carefully understand that the total number of hours in the day can never be more that 24 hours. based on this important fact the answer to the question can be very easily deduced. The only requirement is calculating perfectly.
Number of hours in a day = 24 hours
Percentage of hours of sleep in a day = 33%
Amount of sleep in the day = (33/100) * 24
= 7.92 hours
So 33% of sleep in a day is equal to 7.92 hours. I hope this answer has helped you. In future you can keep the procedure in mind for solving such problems.