Question 31636: Question:
Account bumbers for Northern Oil COmpany consist of nin digits. If the fist digit cannot be a 0, or a 1, how many account numbers are possible.
(A) 8,000,000,000
(B) 900,000,000
(C) 800,000,000
(D) 1,000,000,000
Thank you in advanced for your help.
Answer by mbarugel(146)   (Show Source):
You can put this solution on YOUR website! Hello!
For each digit (except the first one) there are 10 values to choose from (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). Let's ignore for now the first digit.
We know that:
The 2nd digit can be any of 10 values
The 3rd digit can be any of 10 values
...
The 9th digit can be any of 10 values
So there are 10^8 (10 possible values for each of the 8 digits) = 100,000,000 possible account numbers. However, we must take in account the 1st digit. For this digit, there are 8 possible values (2, 3, 4, 5, 6, 7, 8, 9). So for each of the 100,000,000, there are 8 possible ways to choose the 1st digit. Therefore, the total number of possible accounts is 800,000,000
I hope this helps!
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