or

a ray reflected successively from two plane mirrors inclined at a certain angle undergoes a deviation of 300. Then the angle is

a) 30    b) 60    c) 90    d 120

      , ∠ABD=y 

Here AD and BD are Normal lines,

      
              
Total deviation is  
                             
                             


Here from the question deviation angle is 300o

let, a be the angle between two plane mirror,

     therefore, 

                300o = 360o - 2a

             so, a= 30o