Question

size of the image by a mirror having a focal length of 20 cm is observed to be reduced to one third of its size the distance at which mirror is placed from the object nature of image and type of mirror respectively are

Answer 1

F = 20cm
height of image = 3 height of object   h1/h0 = -v/u   
3h0/h0 = -v/u
v = -3u 
1/v + 1/u = 1/20
u = 13.3 cm 
v = 1/20 - 1/13.3 
v = -0.025cm