Discrete Math Question Q02 P288 Textbook Mathematical Struct

Discrete Math Question (Q02, P288, Textbook: Mathematical Structures for Computer Science 7e):

Compute the value of the following expressions:

Solution

As per the P(n,r) rule

P(n,r)=n!/(n-r)!

(a) P(7,2)= 7!/(7-2)!

= (1x2x3x4x5x6x7)/(1x2x3x4x5)

= 6x7=42

(b)

P(8,5)= 8!/(8-5)!

= (1x2x3x4x5x6x7x8)/(1x2x3)

= 4x5x6x7x8=6720