The magnifying power of a telescope with tube length 60cm is 5. What is the focal length of its eye piece?

$\begin{array}{l}Magnifying power =m=\frac{f_o}{f_e} \text{}\\ \Rightarrow 5=\frac{f_o}{f_e} \text{}\\ \Rightarrow f_o=5f_e\\ \\ Length of tube = f_o+f_e=60cm \text{}\\ \Rightarrow 6f_e=60 \text{}\\ \Rightarrow f_e=10 cm\end{array}$