SOLUTION: How many 7-digit numbers can be formed if the first digit cannot be 0 or 9 and if the last digit is greater than or equal to 4 and less than or equal to 5? Repeated digits are allo
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Question 412777: How many 7-digit numbers can be formed if the first digit cannot be 0 or 9 and if the last digit is greater than or equal to 4 and less than or equal to 5? Repeated digits are allowed.
I do not even remotley understand how to start this problem. Please explain how you got the answer so that I can learn this. Answer by solver91311(24713) (Show Source):
You don't even remotely know how to spell remotely -- you are in big trouble.
Since 0 and 9 are excluded from the first digit, there are 8 choices left. For each of those 8 choices we can choose any digit we like for the second digit, so we have 10 choices. 8 times 10 is 80 possibilities for the first two digits. For each of those 80 possibilities, we have 10 choices for the third digit: 800 choices. And so on...
gets you the number of choices for the first 6 digits.
Finally, you come to the last digit. Greater than or equal to 4 and less than or equal to 5. The last digit can either be 4 or 5, which is to say two choices.
Final tally:
You get to do your own arithmetic.
John
My calculator said it, I believe it, that settles it
