Answer
$P(5,2)=20$
Work Step by Step
The permutations of 5 objects a,b,c,d and e taken 2 at a time is
$ab,ac,ad,ae,ba,bc,bd,be,ca,cb,cd,ce,da,db,dc,de,ea,eb,ec,ed$
Use the permutation formula to obtain:
$P(5,2)=\frac{5!}{(5-2)!}=\frac{5!}{3!}=\frac{5\cdot4\cdot3!}{3!}=20$
$P(5,2)=20$
