Question:
Four letters E, K, S and V, one in each, were purchased from a plastic warehouse. How many ordered pairs of letters, to be used as initials, can be formed from them?
Solution:
Here, we need to find out the number of pairs of the letters that can be formed with the 4 letters.
Required number of ordered pairs = Number of arrangements of four letters, taken two at a time = 4P2
$=\frac{4 !}{(4-2) !}$
$=\frac{4 !}{2 !}$
$=\frac{4 \times 3 \times 2 !}{2 !}$
$=4 \times 3$
$=12$