If lenses are placed in contact, the focal length of single equivalent length can be given as
`(1)/(f)=(1)/(f_(1))+(1)/(f_(2))=(1)/(10)-(1)/(20)=(1)/(20)`
`rArr f=+20`
Now using lens formula considering system of lenses as a single lens, we get
`(1)/(v)-(1)/(u)=(1)/(f)`
`:. (1)/(v)=(1)/(-10)=(1)/(20)`
`(1)/(v)=(1)/(20)-(1)/(10)=(-1)/(20)rArrv=-20cm`
Now using magnification formula, we get
`m=(-20)/(-10)=2`
