An object is placed in front of a concave mirror of focal length 20cm .The image formed is 3 times

use the formula m = -v/u this will give two values of v interms of u

now use the formula 1/v + 1/u = 1/f

put the values of f , v interms of u and calculate value of u which is ans. for real image use v = +3u for virtual image use v=-u this will give two positions