Chapter 11 - Probability and Statistics - 11-1 Permutations and Combinations - Practice and Problem-Solving Exercises - Page 678: 22

$56$

Use the formula $P(n,r)=\dfrac{n!}{(n-r)!}$. Here we have $n=8$ and $r=2$. Substitute these values into the formula above to obtain: $P(8,2)=\dfrac{8!}{(8-2)!}\\$ $P(8,2)=\dfrac{8!}{6!}\\$ $P(8,2)=\dfrac{8*7*6*5*4*3*2*1}{6*5*4*3*2*1}\\$ Cancel out common factors to obtain: $P(8, 2) = 8 \cdot 7 = 56$