There is a safe that has a passcode of three digits. Every digit can be a number from 0 to 9, except the first digit which can't be 0 and should be in range 1 to 9. (a) How many passcode is possible to create? (For example, valid passcode is 109, or 246, or 950, ...) (b) How many passcode is possible to create if you can't use a number more than once? (If you use 3 for the first digit, you can't use it for the second and third digit) (c) How many passcode is possible to create if the first digit is 1? (For example, valid passcode is 142, or 103, or 193, ...)

A First Course in Probability (10th Edition)
10th Edition
ISBN:9780134753119
Author:Sheldon Ross
Publisher:Sheldon Ross
Chapter1: Combinatorial Analysis
Section: Chapter Questions
Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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Hi! I need a solution for this problem:

There is a safe that has a passcode of three digits. Every digit can be a number from 0 to 9, except the first digit which can't be 0 and should be in range 1 to 9.

(a) How many passcode is possible to create? (For example, valid passcode is 109, or 246, or 950, ...)

(b) How many passcode is possible to create if you can't use a number more than once? (If you use 3 for the first digit, you can't use it for the second and third digit)

(c) How many passcode is possible to create if the first digit is 1? (For example, valid passcode is 142, or 103, or 193, ...)

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