A concave mirror of focal length 20cm is placed 50cm from a wall. How far from the wall an object is placed to form its real image on the wall?

Explanation

V=-50cm F=-20cm
From mirror formula 1/u=1/f-1/v=-1/20+1/50=-3/100
U=-33.3cm
Therefore the distance of the object from the wall x=50-u
X=50-33.3=167.7cm