Solution
= Solution
By the <multiplication principle>, the successive places have six, five, four, three, two and one available letters. Thus the number of <permutations> is
$$
\boxed{6!=720}.
$$
= Solution
By the <multiplication principle>, the successive places have six, five, four, three, two and one available letters. Thus the number of <permutations> is
$$
\boxed{6!=720}.
$$