41.
$$\eqalign{ & {\text{If}}\,\,{\log _7}{\log _5}\left( {\sqrt {x + 5} + \sqrt x } \right) = 0, \cr & {\text{what}}\,\,{\text{is}}\,\,{\text{the}}\,\,{\text{value}}\,\,{\text{of}}\,\,x? \cr} $$

42.
$$\eqalign{ & {\text{If}}\,{\text{a = lo}}{{\text{g}}_{\text{8}}}{\text{225}}\,{\text{and}}\,{\text{b = lo}}{{\text{g}}_{\text{2}}}{\text{15}}, \cr & {\text{then}}\,a\,{\text{in}}\,{\text{terms}}\,{\text{of}}\,b\,{\text{is}} - \cr} $$

43.
$$\eqalign{ & {\text{If}}\,\log 2 = 0.3010\,and\,\log 3 = 0.4771, \cr & the\,value\,of\,{\log _5}512 = ? \cr} $$

44.
$$\eqalign{ & {\text{If the logarithm of a number is - 3}}{\text{.153,}} \cr & {\text{what are characteristic and mantisa?}} \cr} $$

45.
$$\eqalign{ & {\text{If}}\log 2 = 0.30103, \cr & {\text{the}}\,{\text{number}}\,{\text{of}}\,{\text{digits}}\,{\text{in}}\,{4^{50}}{\text{is}} - \cr} $$