Question 1116174
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For case b) I have another solution and different  answer.


<pre>
    The two last digits must be "25", or "50" or "75"  (00 does not work, since repetitions are not allowed).


    If the last two digits are "25", then the first digit can be any of only 7 digits  1, 3, 4, 6, 7, 8, 9.


    If the last two digits are "50", then the first digit can be any of 8 digits  1, 2, 3, 4, 6, 7, 8, 9.


    If the last two digits are "75", then the first digit can be any of only 7 digits  1, 2, 3, 4, 6, 8, 9.


    In all, there are  7 + 8 + 7 = 22 opportunities for the first digit and, correspondingly, 22 three-digit numbers

    satisfying the condition.
</pre>