15. In a certain month, the dates of three of the Sundays are prime. On what day does the 7th of the month fall?
A Thursday
B Friday
C Saturday
D Monday
E Tuesday
SolUtion
The diagram below shows a calendar for a month with dates that are prime shown in bold. It can be seen that the only column with three dates shown in bold is Column C. Therefore if a month has three Sundays with dates that are prime, that month has 31 days in it and the dates of the Sundays are the 3rd, 10th, 17th, 24th and 31st of that month. If the 3rd is a Sunday, then the 4th is a Monday, the 5th is a Tuesday and the 6th a Wednesday. Hence the 7th of the month is a Thursday.