Question

Find the number of permutations of the first ten letters of the alphabet taking two letters at a time

Answer 1

\[nPr=\frac{ n! }{(n-r)! }\]

\[n=10\] and \[r=2\]

\[10P2=\frac{ 10! }{ (10-2)! }\]

\[10P2=\frac{ 10*9*8! }{ 8! }\]

\[10P2=10*9\]

\[10P2=90\]

90 Ways