At what distance from a convex lens of focal length 5 m should a boy stand so that his image is half his height ?

Explanation

Data : Convex lens ,`f=2.5` m,
`M=-1/2, u=?`
`M=-1/2 =v/u therefore v=- u/2`
`1/f=1/v -1/u=1/(-(u)/(2))-1/u`
`- 2/u-1/u=- 3/u`
`therefore u=-3f=-3xx5 m =-15 m`
This is the object distance .
The boy should stand at 15m from the convex lens so that his image is half his height.