In how many different ways can the letters of "SUNDAY" be arranged?
6 choices for the 1st letter, "S,U,N,D,A,Y" for which there are
5 choices for the 2nd letter, for which there are
4 choices for the 3rd letter, for which there are
3 choices for the 4th letter, for which there are
2 choices for the 5th letter, for which there are
1 choice for the 6th letter.
That's 6∙5∙4∙3∙2∙1 = 6! = 720 ways
How many of these arrangements being with "S"?
1 choice for the 1st letter, "S", for which there are
5 choices for the 2nd letter, "U,N,D,A,Y", for which there are
4 choices for the 3rd letter, for which there are
3 choices for the 4th letter, for which there are
2 choices for the 5th letter, for which there are
1 choice for the 6th letter.
That's 1∙5∙4∙3∙2∙1 = 1∙5! = 120 ways
How many begin with "S" but do not end with vowel?
1 choice for the 1st letter, "S", for which there are
2 choices for the 6th letter, "U,A", for which there are
4 choices for the 2nd letter, for which there are
3 choices for the 3rd letter, for which there are
2 choices for the 4th letter, for which there are
1 choice for the 5th letter.
That's 1∙2∙4∙3∙2∙1 = 2∙4! = 4∙24 = 96 ways
Edwin