To find the number of possible phone numbers, we need to consider the number of options for each digit and whether repetitions are allowed or not.
1. Without repetition:
In this case, once we use a digit, we cannot use it again. For the first digit, we have 10 options (0-9), for the second digit, we have 9 options (excluding the already used digit), and so on. Thus, the number of possible phone numbers without repetition is calculated as:
Number of options for the first digit * Number of options for the second digit * ... * Number of options for the last digit.
So, the total number of possible phone numbers without repetition is: 10*9*8*7*6*5 = 151,200.
2. With repetition:
In this case, we can use the same digit multiple times. For each digit, we still have 10 options (0-9). Therefore, the number of possible phone numbers with repetition is calculated as:
Number of options for each digit^(Number of digits)
So, the total number of possible phone numbers with repetition is: 10^7 = 10,000,000.
Therefore, without repetition, there are 151,200 possible phone numbers, and with repetition, there are 10,000,000 possible phone numbers.