The focal length of a concave mirror, that produces four times larger real image of an object placed at 5 cm distance from the mirror, is------

Answer 1

u=-5cm
f= ?
m=-4
magnification will be negative as the image is real.
m=-v/u
-4=-v/-5
v=-20
1/f= 1/v+ 1/u
1/f= -1/20-1/5
1/f= -1-4/20
1/f=-5/20
f= 4

Answer 2

The focal length of the concave mirror is 4 cm.