6.
$${\rm{If}}{\kern 1pt} \,{\kern 1pt} {\log _{10}}7 = a,{\kern 1pt} {\kern 1pt} {\rm{then}}\,{\kern 1pt} {\kern 1pt} {\log _{10}}\left( {{1 \over {70}}} \right){\rm{is}}\,{\kern 1pt} {\rm{equal}}\,{\kern 1pt} {\rm{to}}$$

7.
If log10 2 = 0.3010, then log2 10 is equal to:

8.
If log10 2 = 0.3010, the value of log10 80 is:

9.
$$\eqalign{ & {\text{If}} \Rightarrow {\log _{10}}5 + {\log _{10}}\left( {5x + 1} \right) = {\log _{10}}\left( {x + 5} \right) + 1, \cr & {\text{then}}\,x\,{\text{is}}\,{\text{equal}}\,{\text{to}}: \cr} $$

10.
$$\eqalign{ & {\text{The}}{\kern 1pt} {\text{value}}{\kern 1pt} {\text{of}} \cr & \left( {\frac{1}{{{{\log }_3}60}} + \frac{1}{{{{\log }_4}60}} + \frac{1}{{{{\log }_5}60}}} \right){\text{is}}: \cr} $$