$\sum\limits_{n = 1}^n {{1 \over {{{\log }_{{2^n}}}(a)}}} = $
${{n(n + 1)} \over 2}{\log _a}2$
${{n(n + 1)} \over 2}{\log _2}a$
${{{{(n + 1)}^2}{n^2}} \over 4}{\log _2}a$
None of these
${\log _4}18$ is
The set of real values of $x$ for which ${\log _{0.2}}{{x + 2} \over x} \le 1$ is
If ${\log _5}a.{\log _a}x = 2,$then $x$ is equal to
The number of solution of ${\log _2}(x + 5) = 6 - x$ is
If $a = {\log _{24}}12,\,b = {\log _{36}}24$ and $c = {\log _{48}}36,$ then $1+abc$ is equal to