Question 1046732
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In all, there are 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.


Zero is prohibited in the first position.


No other restrictions.


9 options for the first position and 10 options for any of 2-nd, 3-rd and 4-th position.


The number of combinations is {{{9*10^3}}} = 9000.