Two converging lenses of focal lengths $f_1=10 cm$ and $f_2=20 cm$ are placed at some separation. A parallel beam of light is incident of $1^{st}$ lens then 

If lenses are placed at such a separation that emergent beam from 2nd lens is parallel. then emergent beam width is 2 cm if original beam has a width of 1 cm. 

For emergent beam from $2^{nd}$ lens to be parallel the separation between the lenses has to be $60 cm$. 

for emergent beam form $2^{nd}$ lends to be parallel the separation between the lenses has to be $30 cm$.

If lenses are placed at such a separation that emergent beam from 2nd lens is parallel, then emergent beam width is 4 cm if original beam width is 1 cm.