If $${\log _{10}}7 = a,$$ then $${\log _{10}}\left( {\frac{1}{{70}}} \right)$$ is equal to
A. - (1 + a)
B. (1 + a)-1
C. $$\frac{a}{10}$$
D. $$\frac{1}{10a}$$
Answer: Option A
Solution(By Examveda Team)
$$\eqalign{ & {\log _{10}}\left( {{1 \over {70}}} \right) \cr & = {\log _{10}}1 - {\log _{10}}70 \cr & = - {\log _{10}}\left( {7 \times 10} \right) \cr & = - \left( {{{\log }_{10}}7 + {{\log }_{10}}10} \right) \cr & = - \left( {a + 1} \right) \cr} $$This Question Belongs to Arithmetic Ability >> Logarithm
When I entered option A, it says incorrect. But the answer says Option A.