Chapter 13 - Counting and Probability - 13.2 Permutations and Combinations - 13.2 Asses Your Understanding - Page 855: 25

$123,124,134,132,142,143$ $213,214,231,234,241,243$ $312,314,321,324,341,342$ $412,413,421,423,431,432$ $P(4,3)=24$

The ordered arrangements: $123,124,134,132,142,143$ $213,214,231,234,241,243$ $312,314,321,324,341,342$ $412,413,421,423,431,432$ We know that $P(n,r)=n(n-1)(n-2)...(n-k+1).$ Also $P(n,0)=1$ by convention. Hence $P(4,3)=4\cdot3\cdot2=24$.