28. How many four-letter "words" can you make if no letter is used twice and each word must contain at least one vowel (A, E, I, O or U)?

37. A BINGO card is a 5 by 5 grid. The center square is a free space and has no number. The first column is filled with five distinct numbers from 1 to 15, the second with five from from 16 to 30, the middle column with four numbers from 31 to 45, the fourth with five numbers from 46 to 60, and the fifth with five numbers from 61 to 75. Since the object of the game is to get five in a row horizontally, vertically or diagonally the order is important. How many BINGO cards are there?

44. How many ways can 5 history books, 3 math books, and 4 novels be arranged on a shelf if the books of each type must be together?