11. If the month of July has 5 Tuesdays, and three of them fall on even-numbered days,what is the date of the third Tuesday in July?
12. A box contains 20 yellow discs, 9 red discs, and 6 blue discs. If discs are selected at random, then the smallest number of discs that need to be selected to be assured of selecting at least two discs of each color is?
13. If \(a@b = \frac{a+b}{a-b}\) , find n such that \(3@n = 3\).
14. Find all real values of \(x\) for which \(\sqrt{4x^2 + 12x + 9} = 2x + 3\).
15. Find the number of positive factors of 2020.