Answer
90
Work Step by Step
$_{10}$P$_{2}$ is a permutation. To solve, use the permutation formula:
$_{n}$P$_{r}$ = $\frac{n!}{(n-r)!}$
Plug in 10 for "n" and 2 for "r":
$_{n}$P$_{r}$ = $\frac{n!}{(n-r)!}$
$_{10}$P$_{2}$ = $\frac{10!}{(10-2)!}$ = $\frac{10!}{8!}$ = $\frac{10\times9\times8\times7\times6\times5\times4\times3\times2\times1}{8\times7\times6\times5\times4\times3\times2\times1}$
As 8x7x6x5x4x3x2x1 appears in both the numerator and denominator, we can cancel out these numbers. We are then left with:
10 x 9 = 90
