Homework Sourse41 We will use the letters a b c d e f to form words of leng
(4.1) We will use the letters a; b; c; d; e; f to form words of length 4. Letters cannot be repeated.
(a) How many words can be made?
(b) How many words end in ef?
(c) How many words contain ef as consecutive letters?
(d) How many words contain both e and f, but not necessarily consecutively?
(e) How many words contain an e or an f (or both)?
Solution
A. we have total 6 letters.
6*5*4*3 as 1st position is open for all 6 ways, then 5 ways and so on till 4th letter is filled
=360 words
B. position of ef is fixed
hence 6*5*1*1=30
C. ef is consecutive so let it be one word.
6*5*4
=120
D. 360-120=240
E.240+120=360
