The value of 1 _360 + 1 _460 + 1 _560 is :

Answer: Option B

Given expression
$$\begin{array}{rl}& ={\log }_{60}3+{\log }_{60}4+{\log }_{60}5\\ & ={\log }_{60}\left(3\times 4\times 5\right)\\ & ={\log }_{60}60\\ & =1\end{array}$$