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# How many 10 digit numbers can be written using digits (9 and 2) ?

$\begin{array}{1 1}(A)\;10C_1+9C_2\\(B)\;2^{10}\\(C)\;10C_2\\(D)\;10!\end{array}$

Total number of numbers =$2\times 2.....\times 10$ times
$\Rightarrow 2^{10}$
Hence (B) is the correct answer.