.
In a certain region all license plates are composed of three letters followed by three numbers,
or three numbers followed by three letters. The only restriction is that zero can never be
the first of the three numbers if the three numbers come first.
Find how many license plates are possible.
~~~~~~~~~~~~~~~~~~~~~~~~
From the first glance, I see that this solution in the referred source is overcomplicated.
I mean, the logic is overcomplicated.
Therefore, I developed my own simple (adequately simple) solution, in 3 clear steps.
(1) if 3 digits go first, followed by 3 letters, with the imposed restrictions,
then the number of plates is 9*10*10*26*26*26 = 15818400.
(2) if 3 letters go first, followed by 3 digits (no restrictions in this case)
then the number of plates is 26*26*26*10*10*10 = 17576000.
(3) The answer is the sum of these numbers 15818400 + 17576000 = 33394400.
Solved.
----------------
Now I see that the referred solution is not only overcomplicated - it is INCORRECT, in addition.
///////////////
Formulation of the problem is not perfect.
To be accurate Math formulation, the term " number " should be replaced by " digit " everywhere.
\\\\\\\\\\\\\\\\\\\
For the sake of next generations of students I submitted this my solution under the referred link.