Pen Arrangements
How many ways can 4 different pens be arranged on a desk?
Expand Hint
The number of different permutations of "n" distinct objects taken "r" at a time is:
$$$P_{(n,r)}=\frac{n!}{(n-r)!}$$$
Hint 2
For zero factorial:
$$$0! = 1$$$
The number of different permutations of "n" distinct objects taken "r" at a time is:
$$$P_{(n,r)}=\frac{n!}{(n-r)!}$$$
A permutation is an arrangement or sequence of selections of objects from a single set. Unlike a combination, the order in which elements are selected or arranged is significant. In this problem, there are 4 distinct objects (
$$n=4$$
) that are placed on the desk sequentially to make a single arrangement (
$$r=4$$
). Thus,
$$$P_{(4,4)}=\frac{4!}{(4-4)!}=\frac{4!}{0!}=\frac{4\cdot 3 \cdot 2 \cdot 1}{1}=24$$$
24
Time Analysis
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