In a certain month the 5th falls on a Tuesday. What is the date of the third Sunday of that month?

Step back from Tuesday the 5th: the 4th is a Monday and the 3rd is a Sunday. The Sundays of the month are therefore the 3rd, 10th, 17th, 24th and 31st, and the third of those is the 17th. The traps: 10th is the second Sunday, reached by treating the 3rd as though it did not count; 24th is the fourth Sunday, reached by calling the 3rd 'Sunday number zero'; 19th comes from reading the 5th itself as the Sunday, which gives the wrong list 5th, 12th, 19th.