Question 1169539
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Use the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 to determine how many three digit numbers are possible 
when there are NO restrictions and {{{highlight(cross(numbers))}}} <U>digits</U> CAN be repeated.
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<pre>
Any non-zero digit in the left-most position: 9 options;


any of 10 digit in the next (2nd) position: 10 options;


any of 10 digit in the next (3rd) position: 10 options.



These selections are independent for each of the 3 positions - - - so, according to the Fundamental Counting Principle,

there are 9*10*10 = 900 different three-digit numbers.



You can calculate it in other way by noticing that  900 is  1000 (all possible 3-digit combinations, 
including 0 in the left-most position)  _MINUS_  3-digit words starting from 0.
</pre>

Solved and answered using two methods for your better understanding.