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How many two-digit numbers are divisible by $3$ but not by $6$? 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying of Multiplication and Division
There are $99$ $4-3 = 33$-multiples of $3$ less than $100$.  $3$ of them are one-digit numbers: $3$, $6$ and $9$.  Hence there are $30$ $2$-digit multiples of $3$.  Similarly, there are $96 + 6 -1 = 16 -1 = 15$ $2$-digit multiples of $6$.  Hence, the answer is 30 - 15 = \textbf{15.}  Answer： \textbf{(B)} 