For any two numbers m , n ; (m+n) : (m-n) : mn = 7: 1: 60 . Find the value of 1/m : 1/n

$\frac{m+n}{m-n}=\frac{7x}{x} \Rightarrow \frac{m}{n}=\frac{4x}{3x}$  

Again    $mn=12x2$ 

and         mn =60x  

so,  $60x=12x2 \Rightarrow x=5$    

=>  m= 20  and    n= 15

Hence,     $\frac{1}{m}:\frac{1}{n}=\frac{1}{20}:\frac{1}{15}=3:4$