Chapter 9.1, Problem 20E

Solution

To state: Whether permutation or combination is described in the situation: 7 digits are selected (without repetition) to form a telephone number

The given situation represents permutation.

Given information:

The given situation is: 7 digits are selected (without repetition) to form a telephone number

Explanation:

Total numbers are: $10\text{or}\left(0,1,2,3,4,5,6,7,8,9\right)$

Number of digits required: 7

It is said that 7 digits are to be selected from 10 digits. It is also given that no digit is to be repeated.

Now note that while selecting the 7 digits order is considered. Order is considered in case of permutation.

For example: A telephone number $1234567$ is definitely different that the mobile number $7654321$ .

Since, order is considered in the given situation, therefore, it is a permutation.