Question:
How many 3-letters words can be formed using a, b, c, d, e if
(i) Repetition of letters is not allowed?
(ii) Repetition of letters is allowed
Solution:
(i) if repetition of letters is not allowed then number of many 3 -letters words that can be formed using $a, b, c, d, e$ are
$5 \times 4 \times 3=60$
(ii) if repetition of letters is allowed then number of many 3-letters words that can be formed using $a, b, c, d$, e are
$5 \times 5 \times 5=125$