The question requires determining the day of the week for December 20th, given information about other dates. To solve this, one would typically calculate the number of days between the known dates and the target date, and then use modulo 7 arithmetic. Since the 5th Monday of April implies a specific date, and the 5th Thursday of November implies another, calculating the day of the week for December 20th can be done by summing the days in the intervening months and adding them to the day of the week of a reference point, then finding the remainder when divided by 7.