Chapter 2 - Section 2-1 - Sample Spaces and Events - Exercises - Page 28: 2-45

(a) 1000 (b) 160 (c) 720

(a) From the multiplication rule, $10^{3} = 1000$ prefixes are possible. (b) From the multiplication rule, $8\times2\times10 = 160$ are possible. (c) Every arrangement of three digits selected from the 10 digits results in a possible prefix. $10P3 = \frac{10!}{(10-3)!} = 720$ prefixes are possible.