Question 1123457
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(1) The units digit has to be odd: how many choices?<br>
(2) The hundreds digit can't be 0; and it can't be the same as the units digit: how many choices?<br>
(3) The tens digit can't be the same as either the units digit or the hundreds digit: how many choices?<br>
By the fundamental counting principle, the number of 3-digit numbers with the specified restrictions is the product of the numbers of choices for each digit.